Bio


My primary research area is coastal water quality, and recently I have expanded my research to include activities on sanitation more broadly. The work on coastal water quality is focused on understanding the sources, transformation, transport, and ecology of biocolloids - specifically fecal indicator organisms, pathogens, and phytoplankton, as well as sources and fate of nitrogen and phosphorus. This knowledge is crucial to directing new policies, and management and engineering practices that protect human and ecosystem health along the coastal margin. The work on sanitation aims to develop microbial risk assessment models to gain a better understanding of how pathogens are transmitted to humans through their contact with water, feces, and contaminated surfaces. Research is focused on key problems in developed and developing countries. The goal is to design and test effective interventions and technologies for reducing the burden of infectious disease.

Academic Appointments


Honors & Awards


  • Chair of West Coast Panel on Ocean Acidification and Hypoxia, States of California, Oregon, Washington, Province of British Colombia (2013-2014)
  • Faculty Fellow Award, UC Irvine (2000-2002)
  • Excellence in Teaching Award, UC Irvine (2001)
  • Visiting Scholar, Pacific Rim Center for Oceans and Human Health (2007)
  • CAREER Award, National Science Foundation (2007)
  • Participant in National Academy of Engineers' Frontiers of Engineering Symposium, National Academy of Engineers (2008)

Professional Education


  • PhD, UC Irvine (2000)

2013-14 Courses


Journal Articles


  • Enteric pathogens in stored drinking water and on caregiver's hands in Tanzanian households with and without reported cases of child diarrhea. PLoS One Mattioli, M., C., Boehm, A., B., Davis, J., Harris, A., R., Mrisho, M., Pickering., A., J. 2014; 9: e84939
  • New performance metrics for quantitative PCR microbial source tracking methods. Environmental Science & Technology Letters Wang, D., Green, H., Shanks, O., Boehm., A., B. 2014; 1: 20-25
  • Performance of forty-one microbial source tracking methods: A twenty-seven lab evaluation study. Water research Boehm, A. B., Van De Werfhorst, L. C., Griffith, J. F., Holden, P. A., Jay, J. A., Shanks, O. C., Wang, D., Weisberg, S. B. 2013; 47 (18): 6812-6828

    Abstract

    The last decade has seen development of numerous new microbial source tracking (MST) methodologies, but many of these have been tested in just a few laboratories with a limited number of fecal samples. This method evaluation study examined the specificity and sensitivity of 41 MST methodologies by analyzing data generated in 27 laboratories. MST methodologies that targeted human, cow, ruminant, dog, gull, pig, horse, and sheep were tested against sewage, septage, human, cow, dog, deer, pig, chicken, pigeon, gull, horse, and goose fecal samples. Each laboratory received 64 blind samples containing a single source (singletons) or two sources (doubletons), as well as diluted singleton samples to assess method sensitivity. Laboratories utilized their own protocols when performing the methods and data were deposited in a central database before samples were unblinded. Between one and seven laboratories tested each method. The most sensitive and specific assays, based on an analysis of presence/absence of each marker in target and non-target fecal samples, were HF183 endpoint and HF183SYBR (human), CF193 and Rum2Bac (ruminant), CowM2 and CowM3 (cow), BacCan (dog), Gull2SYBR and LeeSeaGull (gull), PF163 and pigmtDNA (pig), HoF597 (horse), PhyloChip (pig, horse, chicken, deer), Universal 16S TRFLP (deer), and Bacteroidales 16S TRFLP (pig, horse, chicken, deer); all had sensitivity and specificity higher than 80% in all or the majority of laboratories. When the abundance of MST markers in target and non-target fecal samples was examined, some assays that performed well in the binary analysis were found to not be sensitive enough as median concentrations fell below a minimum abundance criterion (set at 50 copies per colony forming units of enterococci) in target fecal samples. Similarly, some assays that cross-reacted with non-target fecal sources in the binary analysis were found to perform well in a quantitative analysis because the cross-reaction occurred at very low levels. Based on a quantitative analysis, the best performing methods were HF183Taqman and BacH (human), Rum2Bac and BacR (ruminant), LeeSeaGull (gull), and Pig2Bac (pig); no cow or dog-specific assay met the quantitative specificity and sensitivity criteria. Some of the best performing assays in the study were run by just one laboratory so further testing of assay portability is needed. While this study evaluated the marker performance in defined samples, further field testing as well as development of frameworks for fecal source allocation and risk assessment are needed.

    View details for DOI 10.1016/j.watres.2012.12.046

    View details for PubMedID 23880218

  • Simple estimate of entrainment rate of pollutants from a coastal discharge into the surf zone. Environmental science & technology Wong, S. H., Monismith, S. G., Boehm, A. B. 2013; 47 (20): 11554-11561

    Abstract

    Microbial pollutants from coastal discharges can increase illness risks for swimmers and cause beach advisories. There is presently no predictive model for estimating the entrainment of pollution from coastal discharges into the surf zone. We present a novel, quantitative framework for estimating surf zone entrainment of pollution at a wave-dominant open beach. Using physical arguments, we identify a dimensionless parameter equal to the quotient of the surf zone width l(sz) and the cross-flow length scale of the discharge la = M(j) (1/2)/U(sz), where M(j) is the discharge's momentum flux and U(sz) is a representative alongshore velocity in the surf zone. We conducted numerical modeling of a nonbuoyant discharge at an alongshore uniform beach with constant slope using a wave-resolving hydrodynamic model. Using results from 144 numerical experiments we develop an empirical relationship between the surf zone entrainment rate α and l(sz)/(la). The empirical relationship can reasonably explain seven measurements of surf zone entrainment at three diverse coastal discharges. This predictive relationship can be a useful tool in coastal water quality management and can be used to develop predictive beach water quality models.

    View details for DOI 10.1021/es402492f

    View details for PubMedID 24006887

  • Engineering Solutions to Improve the Removal of Fecal Indicator Bacteria by Bioinfiltration Systems during Intermittent Flow of Stormwater. Environmental science & technology Mohanty, S. K., Torkelson, A. A., Dodd, H., Nelson, K. L., Boehm, A. B. 2013; 47 (19): 10791-10798

    Abstract

    Bioinfiltration systems facilitate the infiltration of urban stormwater into soil and reduce high flow events and flooding. Stormwater carries a myriad of pollutants including fecal indicator bacteria (FIB). Significant knowledge gaps exist about the ability of bioinfiltration systems to remove and retain FIB. The present study investigates the ability of model, simplified bioinfiltration systems containing quartz sand and iron oxide-coated quartz sand (IOCS) to remove two FIB (Enterococcus faecalis and Escherichia coli) suspended in synthetic stormwater with and without natural organic matter (NOM) as well as the potential for accumulated FIB to be remobilized during intermittent flow. The experiments were conducted in two phases: (1) the saturated columns packed with either sand or IOCS were contaminated by injecting stormwater with bacteria followed by injection of sterile stormwater and (2) the contaminated columns were subjected to intermittent infiltration of sterile stormwater preceded by a pause during which columns were either kept saturated or drained by gravity. During intermittent flow, fewer bacteria were released from the saturated column compared to the column drained by gravity: 12% of attached E. coli and 3% of attached Ent. faecalis were mobilized from the drained sand column compared to 3% of attached E. coli and 2% attached Ent. faecalis mobilized from the saturated sand column. Dry and wet cycles introduce moving air-water interfaces that can scour bacteria from grain surfaces. During intermittent flows, less than 0.2% of attached bacteria were mobilized from IOCS, which bound both bacteria irreversibly in the absence of NOM. Addition of NOM, however, increased bacterial mobilization from IOCS: 50% of attached E. coli and 8% of attached Ent. faecalis were released from IOCS columns during draining and rewetting. Results indicate that using geomedia such as IOCS that promote irreversible attachment of bacteria, and maintaining saturated condition, could minimize the mobilization of previous attached bacteria from bioinfiltration systems, although NOM may significantly decrease these benefits.

    View details for DOI 10.1021/es305136b

    View details for PubMedID 23721343

  • A Coupled Modeling and Molecular Biology Approach to Microbial Source Tracking at Cowell Beach, Santa Cruz, CA, United States. Environmental science & technology Russell, T. L., Sassoubre, L. M., Wang, D., Masuda, S., Chen, H., Soetjipto, C., Hassaballah, A., Boehm, A. B. 2013; 47 (18): 10231-10239

    Abstract

    Consistently high levels of bacterial indicators of fecal pollution rank Cowell Beach as the most polluted beach in California. High levels of fecal indicator bacteria (FIB), E. coli and enterococci, are measured throughout the summer, resulting in beach advisories with social and economic consequences. The source of FIB, however, is unknown. Speculations have been made that the wrack accumulating on the beach is a major source of FIB to the surf zone. The present study uses spatial and temporal sampling coupled with process-modeling to investigate potential FIB sources and the relative contributions of those sources. Temporal sampling showed consistently high FIB concentrations in the surf zone, sand, and wrack at Cowell Beach, and ruled out the storm drain, the river, the harbor, and the adjacent wharf as the sources of the high concentrations observed in the surf zone. Spatial sampling confirmed that the source of FIB to the beach is terrestrial rather than marine. Modeling results showed two dominant FIB sources to the surf zone: sand for enterococci and groundwater for E. coli. FIB from wrack represented a minor contribution to bacterial levels in the water. Molecular source tracking methods indicate the FIB at the beach is of human and bird origin. The microbial source tracking (MST) approach presented here provides a framework for future efforts.

    View details for DOI 10.1021/es402303w

    View details for PubMedID 23924260

  • A Coupled Modeling and Molecular Biology Approach to Microbial Source Tracking at Cowell Beach, Santa Cruz, CA, United States. Environmental science & technology Russell, T. L., Sassoubre, L. M., Wang, D., Masuda, S., Chen, H., Soetjipto, C., Hassaballah, A., Boehm, A. B. 2013; 47 (18): 10231-10239

    Abstract

    Consistently high levels of bacterial indicators of fecal pollution rank Cowell Beach as the most polluted beach in California. High levels of fecal indicator bacteria (FIB), E. coli and enterococci, are measured throughout the summer, resulting in beach advisories with social and economic consequences. The source of FIB, however, is unknown. Speculations have been made that the wrack accumulating on the beach is a major source of FIB to the surf zone. The present study uses spatial and temporal sampling coupled with process-modeling to investigate potential FIB sources and the relative contributions of those sources. Temporal sampling showed consistently high FIB concentrations in the surf zone, sand, and wrack at Cowell Beach, and ruled out the storm drain, the river, the harbor, and the adjacent wharf as the sources of the high concentrations observed in the surf zone. Spatial sampling confirmed that the source of FIB to the beach is terrestrial rather than marine. Modeling results showed two dominant FIB sources to the surf zone: sand for enterococci and groundwater for E. coli. FIB from wrack represented a minor contribution to bacterial levels in the water. Molecular source tracking methods indicate the FIB at the beach is of human and bird origin. The microbial source tracking (MST) approach presented here provides a framework for future efforts.

    View details for DOI 10.1021/es402303w

    View details for PubMedID 23924260

  • Conducting nanosponge electroporation for affordable and high-efficiency disinfection of bacteria and viruses in water. Nano letters Liu, C., Xie, X., Zhao, W., Liu, N., Maraccini, P. A., Sassoubre, L. M., Boehm, A. B., Cui, Y. 2013; 13 (9): 4288-4293

    Abstract

    High-efficiency, affordable, and low energy water disinfection methods are in great need to prevent diarrheal illness, which is one of the top five leading causes of death over the world. Traditional water disinfection methods have drawbacks including carcinogenic disinfection byproducts formation, energy and time intensiveness, and pathogen recovery. Here, we report an innovative method that achieves high-efficiency water disinfection by introducing nanomaterial-assisted electroporation implemented by a conducting nanosponge filtration device. The use of one-dimensional (1D) nanomaterials allows electroporation to occur at only several volts, which is 2 to 3 orders of magnitude lower than that in traditional electroporation applications. The disinfection mechanism of electroporation prevents harmful byproduct formation and ensures a fast treatment speed of 15 000 L/(h·m(2)), which is equal to a contact time of 1 s. The conducting nanosponge made from low-cost polyurethane sponge coated with carbon nanotubes and silver nanowires ensures the device's affordability. This method achieves more than 6 log (99.9999%) removal of four model bacteria, including Escherichia coli, Salmonella enterica Typhimirium, Enterococcus faecalis, and Bacillus subtilis, and more than 2 log (99%) removal of one model virus, bacteriophage MS2, with a low energy consumption of only 100 J/L.

    View details for DOI 10.1021/nl402053z

    View details for PubMedID 23987737

  • Mechanisms of post-supply contamination of drinking water in Bagamoyo, Tanzania. Journal of water and health Harris, A. R., Davis, J., Boehm, A. B. 2013; 11 (3): 543-554

    Abstract

    Access to household water connections remains low in sub-Saharan Africa, representing a public health concern. Previous studies have shown water stored in the home to be more contaminated than water at the source; however, the mechanisms of post-supply contamination remain unclear. Using water quality measurements and structured observations of households in Bagamoyo, Tanzania, this study elucidates the causal mechanisms of the microbial contamination of drinking water after collection from a communal water source. The study identifies statistically significant loadings of fecal indicator bacteria (FIB) occurring immediately after filling the storage container at the source and after extraction of the water from the container in the home. Statistically significant loadings of FIB also occur with various water extraction methods, including decanting from the container and use of a cup or ladle. Additionally, pathogenic genes of Escherichia coli were detected in stored drinking water but not in the source from which it was collected, highlighting the potential health risks of post-supply contamination. The results of the study confirm that storage containers and extraction utensils introduce microbial contamination into stored drinking water, and suggest that further research is needed to identify methods of water extraction that prevent microbial contamination of drinking water.

    View details for DOI 10.2166/wh.2013.023

    View details for PubMedID 23981881

  • Enterococcus spp on fomites and hands indicate increased risk of respiratory illness in child care centers AMERICAN JOURNAL OF INFECTION CONTROL Julian, T. R., Pickering, A. J., Leckie, J. O., Boehm, A. B. 2013; 41 (8): 728-733

    Abstract

    BACKGROUND: Surface-mediated transmission is a potential route for respiratory disease in child care centers, but evidence of its importance relative to other routes (eg, airborne) is limited. METHODS: We tracked respiratory disease and monitored bacteria contamination on hands and fomites over 4 months during 64 visits at 2 child care centers. Staff monitored health daily by recording respiratory symptoms. We measured concentrations of Escherichia coli, Enterococcus spp, and fecal coliform in hand rinses and on select fomites. RESULTS: We demonstrated that symptomatic respiratory illness was positively associated with microbial contamination on hands and fomites, as measured using Enterococcus spp. Enterococcus spp were 0.28 (95% confidence interval: 0.08-0.48)-log(10) (colony-forming units per 2 hands) higher when an individual had symptomatic respiratory illness. Susceptible individuals were 1.62 (95% confidence interval: 1.06-2.46) times more likely to develop respiratory illness within 4 days with every log(10) increase of Enterococcus spp on hands. CONCLUSION: The findings imply that hand contamination as measured using Enterococcus spp is a risk factor for onset of respiratory illness and highlight the utility of fecal indicator bacteria as a metric for hand and fomite contamination.

    View details for DOI 10.1016/j.ajic.2012.10.013

    View details for Web of Science ID 000322641100014

    View details for PubMedID 23394857

  • Engineered Infiltration Systems for Urban Stormwater Reclamation ENVIRONMENTAL ENGINEERING SCIENCE Grebel, J. E., Mohanty, S. K., Torkelson, A. A., Boehm, A. B., Higgins, C. P., Maxwell, R. M., Nelson, K. L., Sedlak, D. L. 2013; 30 (8): 437-454
  • Salmonella enterica Diversity in Central Californian Coastal Waterways. Applied and environmental microbiology Walters, S. P., González-Escalona, N., Son, I., Melka, D. C., Sassoubre, L. M., Boehm, A. B. 2013; 79 (14): 4199-4209

    Abstract

    Salmonella enterica is one of the most important bacterial enteric pathogens worldwide, however, little is known about its distribution and diversity in the environment. The present study explored the diversity of 104 strains of Salmonella enterica isolated over two years from twelve coastal waterways in central California. Pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were used to probe species diversity. Seventy-four PFGE patterns and 38 sequence types (STs) were found including 18 newly described ST. Nineteen of 25 PFGE patterns were indistinguishable from those of clinical isolates in PulseNet. The most common ST was consistent with S. enterica serovar Typhimurium; other frequently detected STs were associated with serovars Heidelberg and Enteritidis - all important etiologies of salmonellosis. An investigation into S. enterica biogeography was conducted at the level of ST and subspecies. At the ST and subspecies level, we found a taxa-time relationship, but no taxa-area or taxa-environmental distance relationships. STs collected during wet versus dry conditions tended to be more similar; however, STs collected from waterways adjacent to watersheds with similar land covers did not tend to be similar. The results suggest lack of dispersal limitation may be an important factor affecting the diversity of S. enterica in the region.

    View details for DOI 10.1128/AEM.00930-13

    View details for PubMedID 23624479

  • Sunlight Inactivation of Human Viruses and Bacteriophages in Coastal Waters Containing Natural Photosensitizers ENVIRONMENTAL SCIENCE & TECHNOLOGY Silverman, A. I., Peterson, B. M., Boehm, A. B., McNeill, K., Nelson, K. L. 2013; 47 (4): 1870-1878

    Abstract

    Sunlight inactivation of poliovirus type 3 (PV3), adenovirus type 2 (HAdV2), and two bacteriophage (MS2 and PRD1) was investigated in an array of coastal waters to better understand solar inactivation mechanisms and the effect of natural water constituents on observed inactivation rates (k(obs)). Reactor scale inactivation experiments were conducted using a solar simulator, and k(obs) for each virus was measured in a sensitizer-free control and five unfiltered surface water samples collected from different sources. k(obs) values varied between viruses in the same water matrix, and for each virus in different matrices, with PV3 having the fastest and MS2 the slowest k(obs) in all waters. When exposed to full-spectrum sunlight, the presence of photosensitizers increased k(obs) of HAdV2, PRD1 and MS2, but not PV3, which provides evidence that the exogenous sunlight inactivation mechanism, involving damage by exogenously produced reactive intermediates, played a greater role for these viruses. While PV3 inactivation was observed to be dominated by endogenous mechanisms, this may be due to a masking of exogenous k(obs) by significantly faster endogenous k(obs). Results illustrate that differences in water composition can shift absolute and relative inactivation rates of viruses, which has important implications for natural wastewater treatment systems, solar disinfection (SODIS), and the use of indicator organisms for monitoring water quality.

    View details for DOI 10.1021/es3036913

    View details for Web of Science ID 000315326700012

    View details for PubMedID 23384052

  • Comparison of PCR and quantitative real-time PCR methods for the characterization of ruminant and cattle fecal pollution sources. Water Research. Raith, M., Kelty, C., A., Griffith, J., F., Schriewer, A., Wuertz, S., Mieszkin, S., Boehm, A. 2013; 47: 6921-6928
  • Hands and Water as Vectors of Diarrhea! Pathogens in Bagannoyo, Tanzania ENVIRONMENTAL SCIENCE & TECHNOLOGY Mattioli, M. C., Pickering, A. J., Gilsdorf, R. J., Davis, J., Boehm, A. B. 2013; 47 (1): 355-363

    Abstract

    Diarrheal disease is a leading cause of under-five childhood mortality worldwide, with at least half of these deaths occurring in sub-Saharan Africa. Transmission of diarrheal pathogens occurs through several exposure routes including drinking water and hands, but the relative importance of each route is not well understood. Using molecular methods, this study examines the relative importance of different exposure routes by measuring enteric bacteria (pathogenic Escherichia coli) and viruses (rotavirus, enterovirus, adenovirus) in hand rinses, stored water, and source waters in Bagamoyo, Tanzania. Viruses were most frequently found on hands, suggesting that hands are important vectors for viral illness. The occurrence of E. coli virulence genes (ECVG) was equivalent across all sample types, indicating that both water and hands are important for bacterial pathogen transmission. Fecal indicator bacteria and turbidity were good predictors of ECVG, whereas turbidity and human-specific Bacteroidales were good predictors of viruses. ECVG were more likely found in unimproved water sources, but both ECVG and viral genes were detected in improved water sources. ECVG were more likely found in stored water of households with unimproved sanitation facilities. The results provide insights into the distribution of pathogens in Tanzanian households and offer evidence that hand-washing and improved water management practices could alleviate viral and bacterial diarrhea.

    View details for DOI 10.1021/es303878d

    View details for Web of Science ID 000313220300046

    View details for PubMedID 23181394

  • Recommendations following a multi-laboratory comparison of microbial source tracking methods. Water Research. Stewart, J., Boehm, A., B, Dubinsky, E., A., Fong, T., T., Goodwin, K., D., Griffith, J., F. 2013; 47: 6829-6838
  • Performance of Viruses and Bacteriophages for Fecal Source Determination in a Multi-Laboratory, Comparative Study. Water Research. Harwood, V., J., Boehm, A., B., Sassoubre, L., M., Kannappan, V., Stewart, J., R., Fong, T., T. 2013; 47: 6929-6943
  • Multi-Laboratory Evaluations of the Performance of Catellicoccus marimamm\ alium PCR Assays Developed to Target Gull Fecal Sources Water Research. Sinigalliano, C., D., Ervin, J., Van De Werfhorst, L., Badgley, B., Balleste, E., Bartkowiak, J., Boehm, A. 2013; 47: 6883-6896
  • Fecal indicator bacteria on fomites and hands are associated with increased risk of respiratory illness in day care centers. American Journal of Infection Control Julian, T., R., Pickering, A., J., Leckie, J., O., Boehm., A., B. 2013; 41: 728-733
  • Evaluation of the repeatability and reproducibility of a suite of qPCR-based microbial source tracking methods. Water Research. Ebentier, D., L., Hanley, K., T., Cao, Y., Badgley, B., D., Boehm, A., B., Ervin, J., S. 2013; 47: 6839-6848
  • Characterization of fecal concentrations in human and other animal sources by physical, cutlure, and quantitative real-time PCR methods. Water Research. Ervin, J., S., Russell, T., L, Layton, B., A., Yamahara, K., M., Wang, D., Sassoubre, L., M., Boehm, A. 2013; 47: 6873-6882
  • A simple estimate of entrainment rate of pollutants from a coastal discharge into the surf zone. Environmental Science & Technology Wong, S.H., C., Monismith, S., G., Boehm, A., B. 2013; 47: 11554-11561
  • Performance of human fecal-associated PCR-based assays: an international source identificiaiton method evaluation. Water Research. Layton, B., Cao, Y., Ebentie, D., L., Hanley, K., T., Van De Werfhorst, L., Wang, D., Boehm, A. 2013; 47: 6897-6908
  • Enterococcus and Escherichia coli fecal source apportionment with microbial source tracking genetic markers -- Is it feasible? Water Research. Wang, D., Farnleitner, A., H., Field, K., G., Green, H., C., Shanks, O., C., Boehm., A., B. 2013; 47: 6849-6861
  • Mechanisms for Photoinactivation of Enterococcus faecalis in Seawater APPLIED AND ENVIRONMENTAL MICROBIOLOGY Sassoubre, L. M., Nelson, K. L., Boehm, A. B. 2012; 78 (21): 7776-7785

    Abstract

    Field studies in fresh and marine waters consistently show diel fluctuations in concentrations of enterococci, indicators of water quality. We investigated sunlight inactivation of Enterococcus faecalis to gain insight into photoinactivation mechanisms and cellular responses to photostress. E. faecalis bacteria were exposed to natural sunlight in clear, filtered seawater under both oxic and anoxic conditions to test the relative importance of oxygen-mediated and non-oxygen-mediated photoinactivation mechanisms. Multiple methods were used to assess changes in bacterial concentration, including cultivation, quantitative PCR (qPCR), propidium monoazide (PMA)-qPCR, LIVE/DEAD staining using propidium iodide (PI), and cellular activity, including ATP concentrations and expression of the superoxide dismutase-encoding gene, sodA. Photoinactivation, based on numbers of cultivable cells, was faster in oxic than in anoxic microcosms exposed to sunlight, suggesting that oxygen-mediated photoinactivation dominated. There was little change in qPCR signal over the course of the experiment, demonstrating that the nucleic acid targets were not damaged to a significant extent. The PMA-qPCR signal was also fairly stable, consistent with the observation that the fraction of PI-permeable cells was constant. Thus, damage to the membrane was minimal. Microbial ATP concentrations decreased in all microcosms, particularly the sunlit oxic microcosms. The increase in relative expression of the sodA gene in the sunlit oxic microcosms suggests that cells were actively responding to oxidative stress. Dark repair was not observed. This research furthers our understanding of photoinactivation mechanisms and the conditions under which diel fluctuations in enterococci can be expected in natural and engineered systems.

    View details for DOI 10.1128/AEM.02375-12

    View details for Web of Science ID 000309678600032

    View details for PubMedID 22941072

  • Comparison of enterovirus and adenovirus concentration and enumeration methods in seawater from Southern California, USA and Baja Malibu, Mexico JOURNAL OF WATER AND HEALTH Sassoubre, L. M., Love, D. C., Silverman, A. I., Nelson, K. L., Boehm, A. B. 2012; 10 (3): 419-430

    Abstract

    Despite being important etiological agents of waterborne illness, the sources, transport and decay of human viruses in recreational waters are not well understood. This study examines enterovirus and adenovirus concentrations in coastal water samples collected from four beaches impacted by microbial pollution: (1) Malibu Lagoon, Malibu; (2) Tijuana River, Imperial Beach; (3) Baja Malibu, Baja California; and (4) Punta Bandera, Baja California. Water samples were concentrated using a flocculation-based skim milk method and dead-end membrane filtration (MF). Viruses were enumerated using cell culture infectivity assays and reverse transcription quantitative polymerase chain reaction (RT-QPCR). Across concentration and quantification methods, enteroviruses were detected more often than adenoviruses. For both viruses, MF followed by (RT)QPCR yielded higher concentrations than skim milk flocculation followed by (RT)QPCR or cell culture assays. Samples concentrated by skim milk flocculation and enumerated by (RT)QPCR agreed more closely with concentrations enumerated by cell culture assays than MF followed by (RT)QPCR. The detection of viruses by MF and (RT)QPCR was positively correlated with the presence of infectious viruses. Further research is needed to determine if detection of viruses by rapid methods such as (RT)QPCR can be a useful water quality monitoring tool to assess health risks in recreational waters.

    View details for DOI 10.2166/wh.2012.011

    View details for Web of Science ID 000309490300009

    View details for PubMedID 22960486

  • Mobilization and Transport of Naturally Occurring Enterococci in Beach Sands Subject to Transient Infiltration of Seawater ENVIRONMENTAL SCIENCE & TECHNOLOGY Russell, T. L., Yamahara, K. M., Boehm, A. B. 2012; 46 (11): 5988-5996

    Abstract

    This study explores the transport of enterococci (ENT) from naturally contaminated beach sands to the groundwater table via infiltrating seawater using field, laboratory, and modeling experiments. ENT were readily mobilized and transported through the unsaturated zone during infiltration events in both the field and laboratory column experiments. Detachment mechanisms were investigated using a modified version of HYDRUS-1D. Three models for detachment kinetics were tested. Detachment kinetics that are first order with respect to the rate of change in the water content and attached surface bacterial concentrations were found to provide a best fit between predicted and observed data. From these experimental and model results we conclude that detachment mechanisms associated with the rapid increases in pore water content such as air-water interface scouring and thin film expansion are likely drivers of ENT mobilization in the investigated system. These findings suggest that through-beach transport of ENT may be an important pathway through which ENT from beach sands are transported to beach groundwater where they may be discharged to coastal waters via submarine groundwater discharge.

    View details for DOI 10.1021/es300408z

    View details for Web of Science ID 000304783000046

    View details for PubMedID 22533299

  • Fecal Contamination and Diarrheal Pathogens on Surfaces and in Soils among Tanzanian Households with and without Improved Sanitation ENVIRONMENTAL SCIENCE & TECHNOLOGY Pickering, A. J., Julian, T. R., Marks, S. J., Mattioli, M. C., Boehm, A. B., Schwab, K. J., Davis, J. 2012; 46 (11): 5736-5743

    Abstract

    Little is known about the extent or pattern of environmental fecal contamination among households using low-cost, on-site sanitation facilities, or what role environmental contamination plays in the transmission of diarrheal disease. A microbial survey of fecal contamination and selected diarrheal pathogens in soil (n = 200), surface (n = 120), and produce samples (n = 24) was conducted in peri-urban Bagamoyo, Tanzania, among 20 households using private pit latrines. All samples were analyzed for E. coli and enterococci. A subset was analyzed for enterovirus, rotavirus, norovirus GI, norovirus GII, diarrheagenic E. coli, and general and human-specific Bacteroidales fecal markers using molecular methods. Soil collected from the house floor had significantly higher concentrations of E. coli and enterococci than soil collected from the latrine floor. There was no significant difference in fecal indicator bacteria levels between households using pit latrines with a concrete slab (improved sanitation) versus those without a slab. These findings imply that the presence of a concrete slab does not affect the level of fecal contamination in the household environment in this setting. Human Bacteroidales, pathogenic E. coli, enterovirus, and rotavirus genes were detected in soil samples, suggesting that soil should be given more attention as a transmission pathway of diarrheal illness in low-income countries.

    View details for DOI 10.1021/es300022c

    View details for Web of Science ID 000304783000017

    View details for PubMedID 22545817

  • Occurrence and Persistence of Bacterial Pathogens and Indicator Organisms in Beach Sand along the California Coast APPLIED AND ENVIRONMENTAL MICROBIOLOGY Yamahara, K. M., Sassoubre, L. M., Goodwin, K. D., Boehm, A. B. 2012; 78 (6): 1733-1745

    Abstract

    This report documents the presence of fecal indicators and bacterial pathogens in sand at 53 California marine beaches using both culture-dependent and -independent (PCR and quantitative PCR [QPCR]) methods. Fecal indicator bacteria were widespread in California beach sand, with Escherichia coli and enterococci detected at 68% and 94% of the beaches surveyed, respectively. Somatic coliphages and a Bacteroidales human-specific fecal marker were detected at 43% and 13% of the beaches, respectively. Dry sand samples from almost 30% of the beaches contained at least one of the following pathogens: Salmonella spp., Campylobacter spp., Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus (MRSA), which were detected at 15%, 13%, 14%, and 3% of tested beaches, respectively. Fecal indicators and pathogens were poorly correlated to one another and to land cover. Sands were dry at the time of collection, and those with relatively high moisture tended to have higher concentrations or a more frequent occurrence of both indicators and pathogens. Using culture-dependent assays, fecal indicators decayed faster than pathogens in microcosm experiments using unaltered beach sand seeded with sewage and assessed by culture-dependent assays. The following order of persistence was observed (listed from most to least persistent): Campylobacter > Salmonella > somatic coliphages > enterococci > E. coli > F(+) phages. In contrast, pathogens decayed faster than fecal indicators in culture-independent assays: enterococci > Bacteroidales human-specific marker > Salmonella > Campylobacter. Microcosm experiments demonstrated that both indicators and pathogens were mobilized by wetting with seawater. Decay rates measured by QPCR were lower than those measured with culture-dependent methods. Enterococcal persistence and possible growth were observed for wetted microcosms relative to unwetted controls.

    View details for DOI 10.1128/AEM.06185-11

    View details for Web of Science ID 000300629800014

    View details for PubMedID 22247142

  • Coupled physical, chemical, and microbiological measurements suggest a connection between internal waves and surf zone water quality in the Southern California Bight CONTINENTAL SHELF RESEARCH Wong, S. H., Santoro, A. E., Nidzieko, N. J., Hench, J. L., Boehm, A. B. 2012; 34: 64-78
  • Photoinactivation mechanisms of Enterococcus faecalis in seawater. Applied and Environmental Microbiology Sassoubre, L., M., Nelson, K., L., Boehm., A., B. 2012; 78: 7776-7785
  • Diurnal Variation in Enterococcus Species Composition in Polluted Ocean Water and a Potential Role for the Enterococcal Carotenoid in Protection against Photoinactivation APPLIED AND ENVIRONMENTAL MICROBIOLOGY Maraccini, P. A., Ferguson, D. M., Boehm, A. B. 2012; 78 (2): 305-310

    Abstract

    Enterococcus species composition was determined each hour for 72 h at a polluted marine beach in Avalon, Santa Catalina Island, CA. Species composition during the day was significantly different from that at night, based on an analysis of similarity. Enterococcus faecium and E. faecalis were more prevalent at night than during the day, while E. hirae and other Enterococcus species were more prevalent during the day than the night. Enterococcus spp. containing a yellow pigment were more common during the day than the night, suggesting that the pigmented phenotype may offer a competitive advantage under sunlit conditions. A laboratory microcosm experiment established that the pigmented E. casseliflavus isolate and a pigmented E. faecalis isolate recovered from the field site decay slower than a nonpigmented E. faecalis isolate in a solar simulator in simulated, clear seawater. This further supports the idea that the yellow carotenoid pigment in Enterococcus provides protection under sunlit conditions. The findings are in accordance with previous work with other carotenoid-containing nonphotosynthetic and photosynthetic bacteria that suggests that the carotenoid is able to quench reactive oxygen species capable of causing photoinactivation and photostress. The results suggest that using enterococcal species composition as a microbial source tracking tool may be hindered by the differential environmental persistence of pigmented and nonpigmented enterococci.

    View details for DOI 10.1128/AEM.06821-11

    View details for Web of Science ID 000299018800002

    View details for PubMedID 22081569

  • Solar inactivation of four Salmonella serovars in fresh and marine waters JOURNAL OF WATER AND HEALTH Boehm, A. B., Soetjipto, C., Wang, D. 2012; 10 (4): 504-510

    Abstract

    Sunlight-mediated disinfection of water is of interest to both the drinking and recreational water quality community of researchers due to its potential to reduce microbial contamination and waterborne illness. Photo-inactivation of enteric bacteria has primarily been investigated using Escherichia coli and laboratory strains of model bacteria. The present study sought to document the photo-inactivation of environmental isolates of Salmonella in filter-sterilized natural seawater and freshwater and to test the hypothesis that diverse Salmonella serovars decay at similar rates both within and between water matrices. The inactivation of Salmonella enterica Typhimurium LT2, Typhimurium ST19, Heidelberg, and Mbandaka was examined in sunlit and dark microcosms. First order decay was observed in sunlit microcosms; the time until 90% inactivation was of the order of 10 min. A significant shoulder, of the order of 1 hr in length, was observed in the freshwater microcosms during which concentrations were stable. Serovar Mdandaka decayed more slowly than other serovars in both seawater and freshwater. The serovars were extremely stable in the dark microcosms showing little to no decay over 53 days. The results document intra-species variation in photo-inactivation, likely owing to differences in intracellular concentrations of photo-sensitizing molecules or molecules that quench reactive species.

    View details for DOI 10.2166/wh.2012.084

    View details for Web of Science ID 000311341300002

    View details for PubMedID 23165707

  • Quantitative PCR-based detection of pathogenic Leptospira in Hawai'ian coastal streams JOURNAL OF WATER AND HEALTH Viau, E. J., Boehm, A. B. 2011; 9 (4): 637-646

    Abstract

    Pathogenic Leptospira, the causative agents of leptospirosis, are mainly associated with tropical freshwaters, but little is known about their fate in the environment. This study analyzed the distribution of pathogenic Leptospira genomes in 22 tropical coastal streams using quantitative polymerase chain reaction (qPCR). Statistical analyses were conducted to understand pathogenic Leptospira associations with water quality parameters, land use, microbial source tracking (MST) markers, and fecal indicators. Results indicated that pathogenic Leptospira genomes were widespread in O'ahu coastal streams during the Hawai'ian rainy season, with slightly higher concentrations in December when compared with March. Leptospira showed a strong positive association to turbidity, a finding consistent with studies showing increased Leptospira survival when aggregated to particles. Positive correlations to salinity may also indicate survival of Leptospira in relatively saline stream waters. A positive association to the human Bacteroidales fecal marker, no correlation to pig or cow Bacteroidales markers, and a negative association to agricultural land coverage may suggest human or other non-agricultural animal sources of Leptospira (e.g., rats or dogs). Future studies of Leptospira in the Hawai'ian environment are recommended to investigate Leptospira survival in saline waters, to determine both primary and secondary Hawai'ian animal hosts of Leptospira, and to correlate environmental exposures with epidemiological studies of leptospirosis.

    View details for DOI 10.2166/wh.2011.064

    View details for Web of Science ID 000297599300003

    View details for PubMedID 22048423

  • Effective detection of human noroviruses in Hawaiian waters using enhanced RT-PCR methods WATER RESEARCH Tong, H., Connell, C., Boehm, A. B., Lu, Y. 2011; 45 (18): 5837-5848

    Abstract

    The current recreational water quality criteria using growth-based measurements of fecal indicator bacteria (FIB) concentration have their limitations for swimmer protection. To evaluate the possible use of enteric viruses as an improved indicator of human sewage contamination in recreational waters for enhanced health risk assessment, human norovirus (huNoV) was tested as a model in this study. To establish a highly sensitive protocol for effective huNoV detection in waters, 16 published and newly designed reverse transcription polymerase chain reaction (RT-PCR) primer pairs specific for huNoV genogroup I (GI) and genogroup II (GII) were comparatively evaluated side-by-side using single sources of huNoV RNA stock extracted from local clinical isolates. Under optimized conditions, these RT-PCR protocols shared a very different pattern of detection sensitivity for huNoV. The primer sets COG2F/COG2R and QNIF4/NV1LCR were determined to be the most sensitive ones for huNoV GII and GI, respectively, with up to 10(5)- and 10(6)-fold more sensitive as compared to other sets tested. These two sensitive protocols were validated by positive detection of huNoV in untreated and treated urban wastewater samples. In addition, these RT-PCR protocols enabled detection of the prevalence of huNoV in 5 (GI) and 10 (GII) of 16 recreational water samples collected around the island of O'ahu, which was confirmed by DNA sequencing and sequence analysis. Findings from this study support the possible use of enteric viral pathogens for environmental monitoring and argue the importance and essentiality for such monitoring activity to ensure a safe use of recreational waters.

    View details for DOI 10.1016/j.watres.2011.08.030

    View details for Web of Science ID 000296826200003

    View details for PubMedID 21945082

  • Comparison of Surface Sampling Methods for Virus Recovery from Fomites APPLIED AND ENVIRONMENTAL MICROBIOLOGY Julian, T. R., Tamayo, F. J., Leckie, J. O., Boehm, A. B. 2011; 77 (19): 6918-6925

    Abstract

    The role of fomites in infectious disease transmission relative to other exposure routes is difficult to discern due, in part, to the lack of information on the level and distribution of virus contamination on surfaces. Comparisons of studies intending to fill this gap are difficult because multiple different sampling methods are employed and authors rarely report their method's lower limit of detection. In the present study, we compare a subset of sampling methods identified from a literature review to demonstrate that sampling method significantly influences study outcomes. We then compare a subset of methods identified from the review to determine the most efficient methods for recovering virus from surfaces in a laboratory trial using MS2 bacteriophage as a model virus. Recoveries of infective MS2 and MS2 RNA are determined using both a plaque assay and quantitative reverse transcription-PCR, respectively. We conclude that the method that most effectively recovers virus from nonporous fomites uses polyester-tipped swabs prewetted in either one-quarter-strength Ringer's solution or saline solution. This method recovers a median fraction for infective MS2 of 0.40 and for MS2 RNA of 0.07. Use of the proposed method for virus recovery in future fomite sampling studies would provide opportunities to compare findings across multiple studies.

    View details for DOI 10.1128/AEM.05709-11

    View details for Web of Science ID 000295123300023

    View details for PubMedID 21821742

  • Swimmer Risk of Gastrointestinal Illness from Exposure to Tropical Coastal Waters Impacted by Terrestrial Dry-Weather Runoff ENVIRONMENTAL SCIENCE & TECHNOLOGY Viau, E. J., Lee, D., Boehm, A. B. 2011; 45 (17): 7158-7165

    Abstract

    This study used molecular methods to measure concentrations of four enteric viruses (adenovirus, enterovirus, norovirus GI, and norovirus GII) and fecal source tracking markers (human, ruminant, and pig Bacteroidales) in land-based runoff from 22 tropical streams on O'ahu, Hawai'i. Each stream was sampled twice in the morning and afternoon during dry weather. Viruses and human Bacteroidales were widespread in the streams. Watershed septic tank densities were positively associated with higher occurrence of human Bacteroidales and norovirus. There were no associations between occurrence of viruses and fecal indicator concentrations. Virus concentrations and previously reported culturable Salmonella and Campylobacter were used as inputs to a quantitative microbial risk assessment (QMRA) model to estimate the risk of acquiring gastrointestinal (GI) illness from swimming in tropical marine waters adjacent to discharging streams. Monte Carlo methods were used to incorporate uncertainties in the dilution of stream discharge with seawater, swimmer ingestion volumes, pathogen concentrations, and dose-response parameters into the model. Median GI illness risk to swimmers from exposure to coastal waters adjacent to the 22 streams ranged from 0 to 21/1000. GI illness risks from viral exposures were generally orders of magnitude greater than bacterial exposures. Swimming adjacent to streams positive for norovirus or adenovirus resulted in the highest risks. The median risk adjacent to each stream was positively, significantly correlated to the concentration of Clostridium perfringens in the stream. Although a number of important assumptions were made to complete the QMRA, results suggest land-based runoff in the tropics as a potential source of GI illness risk, with pathogens coming from both human and nonhuman nonpoint sources including septic tanks.

    View details for DOI 10.1021/es200984b

    View details for Web of Science ID 000294373400012

    View details for PubMedID 21780808

  • Dissolved Inorganic Nitrogen, Soluble Reactive Phosphorous, and Microbial Pollutant Loading from Tropical Rural Watersheds in Hawai'i to the Coastal Ocean During Non-Storm Conditions ESTUARIES AND COASTS Boehm, A. B., Yamahara, K. M., Walters, S. P., Layton, B. A., Keymer, D. P., Thompson, R. S., Knee, K. L., Rosener, M. 2011; 34 (5): 925-936
  • Using radium isotopes to characterize water ages and coastal mixing rates: A sensitivity analysis LIMNOLOGY AND OCEANOGRAPHY-METHODS Knee, K. L., Garcia-Solsona, E., Garcia-Orellana, J., Boehm, A. B., Paytan, A. 2011; 9: 380-395
  • Sources and fate of Salmonella and fecal indicator bacteria in an urban creek JOURNAL OF ENVIRONMENTAL MONITORING Sassoubre, L. M., Walters, S. P., Russell, T. L., Boehm, A. B. 2011; 13 (8): 2206-2212

    Abstract

    This research aimed to understand the sources and fate of Salmonella and fecal bacteria in urban surface waters. An urban creek (San Pedro Creek, California, USA) that had unusually high levels of Salmonella and fecal bacteria relative to other nearby waterbodies was chosen as a model field site. State of the art microbiological methods were used in concert with modeling to investigate Salmonella and fecal bacteria sources, and determine field-relevant dark inactivation and photoinactivation rates. Three along-creek surveys that spanned reaches adjacent to both urban and forested land covers were conducted to measure Salmonella, enterococci, Escherichia coli, and horse- and human-specific Bacteroidales. Salmonella were detected adjacent to and downstream of urban land cover, but not adjacent to forested land cover. No human or horse-specific Bacteroidales fecal markers were detected implicating other urban animal sources of bacteria. Two locations along the creek where Salmonella was consistently detected were sampled hourly for 25 hours and a mass-balance model was applied to determine field-relevant light and dark inactivation rates for Salmonella, enterococci, and E. coli. Sunlight inactivation did not appear to be important in modulating concentrations of Salmonella, but was important in modulating both enterococci and E. coli concentrations. Dark inactivation was important for all three organisms. This is the first study to quantitatively examine the fate of Salmonella within an urban surface water. Although the work is carried out at a single site, the methodologies are extendable to source tracking in other waterbodies. Additionally, the rate constants determined through the modeling will be useful for modeling these organisms in other surface waters, and represent useful benchmarks for comparison to laboratory-derived inactivation rates.

    View details for DOI 10.1039/c1em10213c

    View details for Web of Science ID 000293502600012

    View details for PubMedID 21687857

  • Wrack promotes the persistence of fecal indicator bacteria in marine sands and seawater FEMS MICROBIOLOGY ECOLOGY Imamura, G. J., Thompson, R. S., Boehm, A. B., Jay, J. A. 2011; 77 (1): 40-49

    Abstract

    Algae on freshwater beaches can serve as reservoirs for fecal indicator bacteria (FIB). Wrack (especially kelp) at marine beaches might sustain FIB as well. This study examines the relationship between beach wrack, FIB, and surrounding water and sediment at marine beaches along the California coast. Surveys of southern and central California beaches were conducted to observe environmental wrack-associated FIB concentrations. FIB concentrations normalized to dry weight were the highest in stranded dry wrack, followed by stranded wet and suspended 'surf' wrack. Laboratory microcosms were conducted to examine the effect of wrack on FIB persistence in seawater and sediment. Indigenous enterococci and Escherichia coli incubated in a seawater microcosm containing wrack showed increased persistence relative to those incubated in a microcosm without wrack. FIB concentrations in microcosms containing wrack-covered sand were significantly higher than those in uncovered sand after several days. These findings implicate beach wrack as an important FIB reservoir. The presence of wrack may increase water and sediment FIB levels, altering the relationship between FIB levels and actual health risk while possibly leading to beach closures. Further work will need to investigate the possibility of FIB growth on wrack and the potential for pathogen presence.

    View details for DOI 10.1111/j.1574-6941.2011.01082.x

    View details for Web of Science ID 000291312500004

    View details for PubMedID 21385189

  • Bacterial pathogens in Hawaiian coastal streams-Associations with fecal indicators, land cover, and water quality WATER RESEARCH Viau, E. J., Goodwin, K. D., Yamahara, K. M., Layton, B. A., Sassoubre, L. M., Burns, S. L., Tong, H., Wong, S. H., Lu, Y., Boehm, A. B. 2011; 45 (11): 3279-3290

    Abstract

    This work aimed to understand the distribution of five bacterial pathogens in O'ahu coastal streams and relate their presence to microbial indicator concentrations, land cover of the surrounding watersheds, and physical-chemical measures of stream water quality. Twenty-two streams were sampled four times (in December and March, before sunrise and at high noon) to capture seasonal and time of day variation. Salmonella, Campylobacter, Staphylococcus aureus, Vibrio vulnificus, and V. parahaemolyticus were widespread -12 of 22 O'ahu streams had all five pathogens. All stream waters also had detectable concentrations of four fecal indicators and total vibrio with log mean ± standard deviation densities of 2.2 ± 0.8 enterococci, 2.7 ± 0.7 Escherichia coli, 1.1 ± 0.7 Clostridium perfringens, 1.2 ± 0.8 F(+) coliphages, and 3.6 ± 0.7 total vibrio per 100 ml. Bivariate associations between pathogens and indicators showed enterococci positively associated with the greatest number of bacterial pathogens. Higher concentrations of enterococci and higher incidence of Campylobacter were found in stream waters collected before sunrise, suggesting these organisms are sensitive to sunlight. Multivariate regression models of microbes as a function of land cover and physical-chemical water quality showed positive associations between Salmonella and agricultural and forested land covers, and between S. aureus and urban and agricultural land covers; these results suggested that sources specific to those land covers may contribute these pathogens to streams. Further, significant associations between some microbial targets and physical-chemical stream water quality (i.e., temperature, nutrients, turbidity) suggested that organism persistence may be affected by stream characteristics. Results implicate streams as a source of pathogens to coastal waters. Future work is recommended to determine infectious risks of recreational waterborne illness related to O'ahu stream exposures and to mitigate these risks through control of land-based runoff sources.

    View details for DOI 10.1016/j.watres.2011.03.033

    View details for Web of Science ID 000291499100002

    View details for PubMedID 21492899

  • Submarine Groundwater Discharge to a High-Energy Surf Zone at Stinson Beach, California, Estimated Using Radium Isotopes ESTUARIES AND COASTS de Sieyes, N. R., Yamahara, K. M., Paytan, A., Boehm, A. B. 2011; 34 (2): 256-268
  • Impact of urbanization and agriculture on the occurrence of bacterial pathogens and stx genes in coastal waterbodies of central California WATER RESEARCH Walters, S. P., Thebo, A. L., Boehm, A. B. 2011; 45 (4): 1752-1762

    Abstract

    Fecal pollution enters coastal waters through multiple routes, many of which originate from land-based activities. Runoff from pervious and impervious land surfaces transports pollutants from land to sea and can cause impairment of coastal ocean waters. To understand how land use practices and water characteristics influence concentrations of fecal indicator bacteria (FIB) and pathogens in natural waters, fourteen coastal streams, rivers, and tidal lagoons, surrounded by variable land use and animal densities, were sampled every six weeks over two years (2008 & 2009). Fecal indicator bacteria (FIB; Escherichia coli and Enterococci) and Salmonella concentrations, the occurrence of Bacteroidales human, ruminant, and pig-specific fecal markers, E. coli O157:H7, and Shiga toxin (stx) genes present in E. coli, were measured. In addition, environmental and climatic variables (e.g., temperature, salinity, rainfall), as well as human and livestock population densities and land cover were quantified. Concentrations of FIB and Salmonella were correlated with each other, but the occurrence of host-specific Bacteroidales markers did not correlate with FIB or pathogens. FIB and Salmonella concentrations, as well as the occurrence of E. coli harboring stx genes, were positively associated with the fraction of the surrounding subwatershed that was urban, while the occurrence of E. coli O157:H7 was positively associated with the agricultural fraction. FIB and Salmonella concentrations were negatively correlated to salinity and temperature, and positively correlated to rainfall. Areal loading rates of FIB, Salmonella and E. coli O157:H7 to the coastal ocean were calculated for stream and river sites and varied with land cover, salinity, temperature, and rainfall. Results suggest that FIB and pathogen concentrations are influenced, in part, by their flux from the land, which is exacerbated during rainfall; once waterborne, bacterial persistence is affected by water temperature and salinity.

    View details for DOI 10.1016/j.watres.2010.11.032

    View details for Web of Science ID 000286995000025

    View details for PubMedID 21168181

  • The Effects of Informational Interventions on Household Water Management, Hygiene Behaviors, Stored Drinking Water Quality, and Hand Contamination in Peri-Urban Tanzania AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE Davis, J., Pickering, A. J., Rogers, K., Mamuya, S., Boehm, A. B. 2011; 84 (2): 184-191

    Abstract

    Safe water storage and hand hygiene have been shown to reduce fecal contamination and improve health in experimental settings; however, triggering and sustaining such behaviors is challenging. This study investigates the extent to which personalized information about Escherichia coli contamination of stored water and hands influenced knowledge, reported behaviors, and subsequent contamination levels among 334 households with less than 5-year-old children in peri-urban Dar es Salaam, Tanzania. One-quarter of the study participants received information about strategies to reduce risk of water- and sanitation-related illness. Respondents in another three study cohorts received this same information, along with their household's water and/or hand-rinse test results. Findings from this study suggest that additional work is needed to elucidate the conditions under which such testing represents a cost-effective strategy to motivate improved household water management and hand hygiene.

    View details for DOI 10.4269/ajtmh.2011.10-0126

    View details for Web of Science ID 000287003900002

    View details for PubMedID 21292883

  • Bacterial hand contamination among Tanzanian mothers varies temporally and following household activities TROPICAL MEDICINE & INTERNATIONAL HEALTH Pickering, A. J., Julian, T. R., Mamuya, S., Boehm, A. B., Davis, J. 2011; 16 (2): 233-239

    Abstract

    To characterize mechanisms of hand contamination with faecal indicator bacteria and to assess the presence of selected pathogens on mothers' hands in Tanzania.A household observational study combined with repeated microbiological hand rinse sampling was conducted among 119 mothers in Dar es Salaam, Tanzania. All hand rinse samples were analysed for enterococci and Escherichia coli, and selected samples were analysed for genetic markers of Bacteroidales, enterovirus and pathogenic E. coli.Using the toilet, cleaning up a child's faeces, sweeping, cleaning dishes, preparing food and bathing were all found to increase faecal indicator bacterial levels on hands. Geometric mean increases in colony forming units per two hands ranged from 50 (cleaning dishes) to 6310 (food preparation). Multivariate modelling of hand faecal indicator bacteria as a function of activities recently performed shows that food handling, exiting the household premises and longer time since last handwashing with soap are positively associated with bacterial levels on hands, while bathing is negatively associated. Genetic markers of Bacteroidales, enterovirus and pathogenic E. coli were each detected on a subset of mothers' hands.Escherichia coli and enterococci on hands can be significantly increased by various household activities, including those involving the use of soap and water. Thus, faecal indicator bacteria should be considered highly variable when used as indicators of handwashing behaviour. This work corroborates hands as important vectors of disease among Tanzanian mothers and highlights the difficulty of good personal hygiene in an environment characterized by the lack of networked sanitation and water supply services.

    View details for DOI 10.1111/j.1365-3156.2010.02677.x

    View details for Web of Science ID 000286116500015

    View details for PubMedID 21091858

  • Hand fecal contamination among Tanzanian mothers varies temporally and following household activities. Tropical Medicine and International Health Pickering, A., J., Julian, T., R., Mamuya, S., Boehm, A., B., Davis, J. 2011; 16: 233-239
  • Contributions of Foot Traffic and Outdoor Concentrations to Indoor Airborne Aspergillus AEROSOL SCIENCE AND TECHNOLOGY Goebes, M. D., Boehm, A. B., Hildemann, L. M. 2011; 45 (3): 352-363
  • Efficacy of alcohol-based hand sanitizer on hands soiled with dirt and cooking oil JOURNAL OF WATER AND HEALTH Pickering, A. J., Davis, J., Boehm, A. B. 2011; 9 (3): 429-433

    Abstract

    Handwashing education and promotion are well established as effective strategies to reduce diarrhea and respiratory illness in countries around the world. However, access to reliable water supplies has been identified as an important barrier to regular handwashing in low-income countries. Alcohol-based hand sanitizer (ABHS) is an effective hand hygiene method that does not require water, but its use is not currently recommended when hands are visibly soiled. This study evaluated the efficacy of ABHS on volunteers' hands artificially contaminated with Escherichia coli in the presence of dirt (soil from Tanzania) and cooking oil. ABHS reduced levels of E. coli by a mean of 2.33 log colony forming units (CFU) per clean hand, 2.32 log CFU per dirt-covered hand, and 2.13 log CFU per oil-coated hand. No significant difference in efficacy was detected between hands that were clean versus dirty or oily. ABHS may be an appropriate hand hygiene method for hands that are moderately soiled, and an attractive option for field settings in which access to water and soap is limited.

    View details for DOI 10.2166/wh.2011.138

    View details for Web of Science ID 000293624300001

    View details for PubMedID 21976190

  • Recombination Shapes the Structure of an Environmental Vibrio cholerae Population APPLIED AND ENVIRONMENTAL MICROBIOLOGY Keymer, D. P., Boehm, A. B. 2011; 77 (2): 537-544

    Abstract

    Vibrio cholerae consists of pathogenic strains that cause sporadic gastrointestinal illness or epidemic cholera disease and nonpathogenic strains that grow and persist in coastal aquatic ecosystems. Previous studies of disease-causing strains have shown V. cholerae to be a primarily clonal bacterial species, but isolates analyzed have been strongly biased toward pathogenic genotypes, while representing only a small sample of the vast diversity in environmental strains. In this study, we characterized homologous recombination and structure among 152 environmental V. cholerae isolates and 13 other putative Vibrio isolates from coastal waters and sediments in central California, as well as four clinical V. cholerae isolates, using multilocus sequence analysis of seven housekeeping genes. Recombinant regions were identified by at least three detection methods in 72% of our V. cholerae isolates. Despite frequent recombination, significant linkage disequilibrium was still detected among the V. cholerae sequence types. Incongruent but nonrandom associations were observed for maximum likelihood topologies from the individual loci. Overall, our estimated recombination rate in V. cholerae of 6.5 times the mutation rate is similar to those of other sexual bacteria and appears frequently enough to restrict selection from purging much of the neutral intraspecies diversity. These data suggest that frequent recombination among V. cholerae may hinder the identification of ecotypes in this bacterioplankton population.

    View details for DOI 10.1128/AEM.02062-10

    View details for Web of Science ID 000286147300019

    View details for PubMedID 21075874

  • Beach wrack is a reservoir for faecal indicator bacteria along the California coast FEMS Microbiology Ecology Imamura, G., Strickfaden, R., M., Boehm, A., B., Jay., J., A. 2011; 77: 40-49
  • A comparison of surface sampling methods for virus recovery from fomites. Applied and Environmental Microbiology Julian, T., R., Tamayo, F., J., Leckie, J., O., Boehm, A., B. 2011; 77: 6918-6925
  • Prominent human health impacts from several marine microbes: History, ecology, and public health implications. International Journal of Microbiology Bienfang, P., K., DeFelice, S., V., Laws, E., A., Brand, L., E., Bidigare, R., R., Christensen, S., Boehm, A. 2011

    View details for DOI 10.1155/2011/152815

  • Virus transfer between fingerpads and fomites JOURNAL OF APPLIED MICROBIOLOGY JULIAN, T. R., Leckie, J. O., Boehm, A. B. 2010; 109 (6): 1868-1874

    Abstract

    Virus transfer between individuals and fomites is an important route of transmission for both gastrointestinal and respiratory illness. The present study examines how direction of transfer, virus species, time since last handwashing, gender, and titre affect viral transfer between fingerpads and glass.Six hundred fifty-six total transfer events, performed by 20 volunteers using MS2, ?X174, and fr indicated 0·23 ± 0·22 (mean and standard deviation) of virus is readily transferred on contact. Virus transfer is significantly influenced by virus species and time since last handwashing. Transfer of fr bacteriophage is significantly higher than both MS2 and ?X174. Virus transfer between surfaces is reduced for recently washed hands.Viruses are readily transferred between skin and surfaces on contact. The fraction of virus transferred is dependent on multiple factors including virus species, recently washing hands, and direction of transfer likely because of surface physicochemical interactions.The study is the first to provide a large data set of virus transfer events describing the central tendency and distribution of fraction virus transferred between fingers and glass. The data set from the study, along with the quantified effect sizes of the factors explored, inform studies examining role of fomites in disease transmission.

    View details for DOI 10.1111/j.1365-2672.2010.04814.x

    View details for Web of Science ID 000284170300002

    View details for PubMedID 20659186

  • Enterococcus species distribution among human and animal hosts using multiplex PCR JOURNAL OF APPLIED MICROBIOLOGY Layton, B. A., Walters, S. P., Lam, L. H., Boehm, A. B. 2010; 109 (2): 539-547

    Abstract

    This study evaluated the use of Enterococcus species differentiation as a tool for microbial source tracking (MST) in recreational waters.Avian, mammalian and human faecal samples were screened for the occurrence of Enterococcus avium, Enterococcus casseliflavus, Enterococcus durans, Enterococcus gallinarum, Enterococcus faecium, Enterococcus faecalis, Enterococcus hirae and Enterococcus saccharolyticus using multiplex PCR. Host-specific patterns of Enterococcus species presence were observed only when data for multiple Enterococcus species were considered in aggregate.The results suggest that no single Enterococcus species is a reliable indicator of the host faecal source. However, Enterococcus species composite 'fingerprints' may offer auxiliary evidence for bacterial source identification.This study presents novel information on the enterococci species assemblages present in avian and mammalian hosts proximate to the nearshore ocean. These data will aid the development of appropriate MST strategies, and the approach used in this study could potentially assist in the identification of faecal pollution sources.

    View details for DOI 10.1111/j.1365-2672.2010.04675.x

    View details for Web of Science ID 000279733700016

    View details for PubMedID 20132375

  • Caffeine and agricultural pesticide concentrations in surface water and groundwater on the north shore of Kauai (Hawaii, USA) MARINE POLLUTION BULLETIN Knee, K. L., Gossett, R., Boehm, A. B., Paytan, A. 2010; 60 (8): 1376-1382

    Abstract

    Caffeine has been associated with wastewater pollution in temperate and subtropical locations, but environmental caffeine concentrations in tropical locations have not been reported. The objectives of this study were to measure caffeine and agricultural pesticide (carbaryl, metalaxyl, and metribuzin) concentrations in environmental waters on the tropical north shore of Kauai (Hawaii, USA) and assess whether patterns in caffeine concentration were consistent with a wastewater caffeine source. Groundwater, river, stream and coastal ocean samples were collected in August 2006 and February 2007. Caffeine was detected in all August 2006 samples and in 33% of February 2007 samples at concentrations up to 88ngL(-1). Metribuzin was detected in five samples collected in February 2007. Carbaryl and metalaxyl were not detected in any sample. Caffeine was not detected in offshore ocean samples or river samples upstream of human development. A positive correlation between caffeine and enterococci suggested a possible wastewater caffeine source.

    View details for DOI 10.1016/j.marpolbul.2010.04.019

    View details for Web of Science ID 000281474000039

    View details for PubMedID 20557899

  • Relationship and Variation of qPCR and Culturable Enterococci Estimates in Ambient Surface Waters Are Predictable ENVIRONMENTAL SCIENCE & TECHNOLOGY Whitman, R. L., Ge, Z., Nevers, M. B., Boehm, A. B., Chern, E. C., Haugland, R. A., Lukasik, A. M., Molina, M., Przybyla-Kelly, K., Shively, D. A., White, E. M., Zepp, R. G., Byappanahalli, M. N. 2010; 44 (13): 5049-5054

    Abstract

    The quantitative polymerase chain reaction (qPCR) method provides rapid estimates of fecal indicator bacteria densities that have been indicated to be useful in the assessment of water quality. Primarily because this method provides faster results than standard culture-based methods, the U.S. Environmental Protection Agency is currently considering its use as a basis for revised ambient water quality criteria. In anticipation of this possibility, we sought to examine the relationship between qPCR-based and culture-based estimates of enterococci in surface waters. Using data from several research groups, we compared enterococci estimates by the two methods in water samples collected from 37 sites across the United States. A consistent linear pattern in the relationship between cell equivalents (CCE), based on the qPCR method, and colony-forming units (CFU), based on the traditional culturable method, was significant (P < 0.05) at most sites. A linearly decreasing variance of CCE with increasing CFU levels was significant (P < 0.05) or evident for all sites. Both marine and freshwater sites under continuous influence of point-source contamination tended to reveal a relatively constant proportion of CCE to CFU. The consistency in the mean and variance patterns of CCE versus CFU indicates that the relationship of results based on these two methods is more predictable at high CFU levels (e.g., log(10)CFU > 2.0/100 mL) while uncertainty increases at lower CFU values. It was further noted that the relative error in replicated qPCR estimates was generally higher than that in replicated culture counts even at relatively high target levels, suggesting a greater need for replicated analyses in the qPCR method to reduce relative error. Further studies evaluating the relationship between culture and qPCR should take into account analytical uncertainty as well as potential differences in results of these methods that may arise from sample variability, different sources of pollution, and environmental factors.

    View details for DOI 10.1021/es9028974

    View details for Web of Science ID 000279304700038

    View details for PubMedID 20527919

  • Nutrient inputs to the coastal ocean from submarine groundwater discharge in a groundwater-dominated system: Relation to land use (Kona coast, Hawaii, USA) LIMNOLOGY AND OCEANOGRAPHY Knee, K. L., Street, J. H., Grossman, E. E., Boehm, A. B., Paytan, A. 2010; 55 (3): 1105-1122
  • Hands, Water, and Health: Fecal Contamination in Tanzanian Communities with Improved, Non-Networked Water Supplies ENVIRONMENTAL SCIENCE & TECHNOLOGY Pickering, A. J., Davis, J., Walters, S. P., Horak, H. M., Keymer, D. P., Mushi, D., Strickfaden, B., Chynoweth, J. S., Liu, J., Blum, A., Rogers, K., Boehm, A. B. 2010; 44 (9): 3267-3272

    Abstract

    Almost half of the world's population relies on non-networked water supply services, which necessitates in-home water storage. It has been suggested that dirty hands play a role in microbial contamination of drinking water during collection, transport, and storage. However, little work has been done to evaluate quantitatively the association between hand contamination and stored water quality within households. This study measured levels of E. coli, fecal streptococci, and occurrence of the general Bacteroidales fecal DNA marker in source water, in stored water, and on hands in 334 households among communities in Dar es Salaam, Tanzania, where residents use non-networked water sources. Levels of fecal contamination on hands of mothers and children were positively correlated to fecal contamination in stored drinking water within households. Household characteristics associated with hand contamination included mother's educational attainment, use of an improved toilet, an infant in the household, and dissatisfaction with the quantity of water available for hygiene. In addition, fecal contamination on hands was associated with the prevalence of gastrointestinal and respiratory symptoms within a household. The results suggest that reducing fecal contamination on hands should be investigated as a strategy for improving stored drinking water quality and health among households using non-networked water supplies.

    View details for DOI 10.1021/es903524m

    View details for Web of Science ID 000277067000014

    View details for PubMedID 20222746

  • Efficacy of Waterless Hand Hygiene Compared with Handwashing with Soap: A Field Study in Dar es Salaam, Tanzania AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE Pickering, A. J., Boehm, A. B., Mwanjali, M., Davis, J. 2010; 82 (2): 270-278

    Abstract

    Effective handwashing with soap requires reliable access to water supplies. However, more than three billion persons do not have household-level access to piped water. This research addresses the challenge of improving hand hygiene within water-constrained environments. The antimicrobial efficacy of alcohol-based hand sanitizer, a waterless hand hygiene product, was evaluated and compared with handwashing with soap and water in field conditions in Dar es Salaam, Tanzania. Hand sanitizer use by mothers resulted in 0.66 and 0.64 log reductions per hand of Escherichia coli and fecal streptococci, respectively. In comparison, handwashing with soap resulted in 0.50 and 0.25 log reductions per hand of E. coli and fecal streptococci, respectively. Hand sanitizer was significantly better than handwashing with respect to reduction in levels of fecal streptococci (P = 0.01). The feasibility and health impacts of promoting hand sanitizer as an alternative hand hygiene option for water-constrained environments should be assessed.

    View details for DOI 10.4269/ajtmh.2010.09-0220

    View details for Web of Science ID 000274263300018

    View details for PubMedID 20134005

  • Microbial and metal water quality in rain catchments compared with traditional drinking water sources in the East Sepik Province, Papua New Guinea JOURNAL OF WATER AND HEALTH Horak, H. M., Chynoweth, J. S., Myers, W. P., Davis, J., Fendorf, S., Boehm, A. B. 2010; 8 (1): 126-138

    Abstract

    In Papua New Guinea, a significant portion of morbidity and mortality is attributed to water-borne diseases. To reduce incidence of disease, communities and non-governmental organizations have installed rain catchments to provide drinking water of improved quality. However, little work has been done to determine whether these rain catchments provide drinking water of better quality than traditional drinking water sources, and if morbidity is decreased in villages with rain catchments. The specific aim of this study was to evaluate the quality of water produced by rain catchments in comparison with traditional drinking water sources in rural villages in the East Sepik Province. Fifty-four water sources in 22 villages were evaluated for enterococci and Escherichia coli densities as well as 14 health-relevant metals. In addition, we examined how the prevalence of diarrhoeal illness in villages relates to the type of primary drinking water source. The majority of tested metals were below World Health Organization safety limits. Catchment water sources had lower enterococci and E. coli than other water sources. Individuals in villages using Sepik River water as their primary water source had significantly higher incidence of diarrhoea than those primarily using other water sources (streams, dug wells and catchments).

    View details for Web of Science ID 000275310700014

    View details for PubMedID 20009255

  • Contrasting spring and summer phytoplankton dynamics in the nearshore Southern California Bight LIMNOLOGY AND OCEANOGRAPHY Santoro, A. E., Nidzieko, N. J., Van Dijken, G. L., Arrigo, K. R., Boehm, A. B. 2010; 55 (1): 264-278
  • Persistence of nucleic acid markers of health-relevant organisms in seawater microcosms: Implications for their use in assessing risk in recreational waters WATER RESEARCH Walters, S. P., Yamahara, K. M., Boehm, A. B. 2009; 43 (19): 4929-4939

    Abstract

    In the last decade, the use of culture-independent methods for detecting indicator organisms and pathogens in recreational waters has increased and has led to heightened interest in their use for routine water quality monitoring. However, a thorough understanding of the persistence of genetic markers in environmental waters is lacking. In the present study, we evaluate the persistence of enterococci, enterovirus, and human-specific Bacteroidales in seawater microcosms. Two microcosms consisted of seawater seeded with human sewage. Two additional seawater microcosms were seeded with naked Enterococcus faecium DNA and poliovirus RNA. One of each replicate microcosm was exposed to natural sunlight; the other was kept in complete darkness. In the sewage microcosms, concentrations of enterococci and enterovirus were measured using standard culture-dependent methods as well as QPCR and RT-QPCR respectively. Concentrations of human-specific Bacteroidales were determined with QPCR. In the naked-genome microcosms, enterococci and enterovirus markers were enumerated using QPCR and RT-QPCR, respectively. In the sewage microcosm exposed to sunlight, concentrations of culturable enterococci fell below the detection limit within 5 days, but the QPCR signal persisted until the end of the experiment (day 28). Culturable enterococci did not persist as long as infectious enteroviruses. The ability to culture enteroviruses and enterococci was lost before detection of the genetic markers was lost, but the human-specific Bacteroidales QPCR signal persisted for a similar duration as infectious enteroviruses in the sewage microcosm exposed to sunlight. In the naked-genome microcosms, DNA and RNA from enterococci and enterovirus, respectively, persisted for over 10d and did not vary between the light and dark treatments. These results indicate differential persistence of genetic markers and culturable organisms of public health relevance in an environmental matrix and have important management implications.

    View details for DOI 10.1016/j.watres.2009.05.047

    View details for Web of Science ID 000272057000017

    View details for PubMedID 19616273

  • Faecal indicator bacteria enumeration in beach sand: a comparison study of extraction methods in medium to coarse sands JOURNAL OF APPLIED MICROBIOLOGY Boehm, A. B., Griffith, J., Mcgee, C., Edge, T. A., Solo-Gabriele, H. M., Whitman, R., Cao, Y., Getrich, M., Jay, J. A., Ferguson, D., Goodwin, K. D., Lee, C. M., Madison, M., Weisberg, S. B. 2009; 107 (5): 1740-1750

    Abstract

    The absence of standardized methods for quantifying faecal indicator bacteria (FIB) in sand hinders comparison of results across studies. The purpose of the study was to compare methods for extraction of faecal bacteria from sands and recommend a standardized extraction technique.Twenty-two methods of extracting enterococci and Escherichia coli from sand were evaluated, including multiple permutations of hand shaking, mechanical shaking, blending, sonication, number of rinses, settling time, eluant-to-sand ratio, eluant composition, prefiltration and type of decantation. Tests were performed on sands from California, Florida and Lake Michigan. Most extraction parameters did not significantly affect bacterial enumeration. anova revealed significant effects of eluant composition and blending; with both sodium metaphosphate buffer and blending producing reduced counts.The simplest extraction method that produced the highest FIB recoveries consisted of 2 min of hand shaking in phosphate-buffered saline or deionized water, a 30-s settling time, one-rinse step and a 10 : 1 eluant volume to sand weight ratio. This result was consistent across the sand compositions tested in this study but could vary for other sand types.Method standardization will improve the understanding of how sands affect surface water quality.

    View details for DOI 10.1111/j.1365-2672.2009.04440.x

    View details for Web of Science ID 000270658100036

    View details for PubMedID 19659700

  • Covariation and Photoinactivation of Traditional and Novel Indicator Organisms and Human Viruses at a Sewage-Impacted Marine Beach ENVIRONMENTAL SCIENCE & TECHNOLOGY Boehm, A. B., Yamahara, K. M., Love, D. C., Peterson, B. M., McNeill, K., Nelson, K. L. 2009; 43 (21): 8046-8052

    Abstract

    Sunlight modulates concentrations of Escherichia coli and enterococci in marine waters. However, the mechanism of photoinactivation is poorly understood. Additionally, little is known about photoinactivation of other fecal indicators and human viruses in recreational waters. We sampled nearshore waters at Avalon Beach, California hourly for 72 h for reactive oxygen species (ROS), traditional indicator bacteria (E. coli and enterococci, and QPCR-based detection of enterococci), F+ (DNA and RNA) and somatic coliphages, the human-specific marker in Bacteroidales (HF marker), human enterovirus, and human adenovirus. E. coli and enterococci (regardless of measurement technique) covaried with each other and the coliphages suggesting similar sources and fates. The occurrence of the HF and enterovirus markers was correlated, but their occurrence was not positively correlated with the other indicators. Lower concentrations or occurrence of all microbes, excluding the HF and enterovirus markers, were observed during sunlit as opposed to dark hours, pointing to the importance of photoinactivation. Empirical-deterministic models for a subset of microbial indicators were created to determine field-relevant sunlight inactivation rates while accounting for time dependent sources and sinks. Photoinactivation rates of enterococci and E. coli, enterococci measured by QPCR, and somatic coliphage were estimated at 7, 6, 3, and 28 d(-1) I(-1), respectively, where I is UVB intensity in W/m(2). Average H(2)O(2) was 183 nM and the maximum singlet oxygen steady state concentration was 6.6 fM. Given the clarity of the water, direct genomic damage of bacteria and coliphage, as well as indirect endogenous damage of bacteria, were likely the most important inactivation mechanisms, but we cannot rule out a contribution by indirect mechanisms involving the H(2)O(2) and singlet oxygen produced exogenously.

    View details for DOI 10.1021/es9015124

    View details for Web of Science ID 000271106300015

    View details for PubMedID 19924921

  • Distribution and diversity of the enterococcal surface protein (esp) gene in animal hosts and the Pacific coast environment JOURNAL OF APPLIED MICROBIOLOGY Layton, B. A., Walters, S. P., Boehm, A. B. 2009; 106 (5): 1521-1531

    Abstract

    This study sought to evaluate the distribution of the enterococcal surface protein (esp) gene in Enterococcus faecium in the Pacific coast environment as well as the distribution and diversity of the gene in Northern California animal hosts.Over 150 environmental samples from the Pacific coast environment (sand, surf zone, fresh/estuarine, groundwater, and storm drain) were screened for the esp gene marker in E. faecium, and the marker was found in 37% of the environmental samples. We examined the host specificity of the gene by screening various avian and mammalian faecal samples, and found the esp gene to be widespread in nonhuman animal faeces. DNA sequence analysis performed on esp polymerase chain reaction amplicons revealed that esp gene sequences were not divergent between hosts.Our data confirm recent findings that the E. faecium variant of the esp gene is not human-specific.Our results suggest that the use of the esp gene for microbial source tracking applications may not be appropriate at all recreational beaches.

    View details for DOI 10.1111/j.1365-2672.2008.04113.x

    View details for Web of Science ID 000264958000012

    View details for PubMedID 19187132

  • Growth of Enterococci in Unaltered, Unseeded Beach Sands Subjected to Tidal Wetting (vol 75, pg 1517, 2009) APPLIED AND ENVIRONMENTAL MICROBIOLOGY Yamahara, K. M., Walters, S. P., Boehm, A. B. 2009; 75 (9): 2997-2997
  • A Model of Exposure to Rotavirus from Nondietary Ingestion Iterated by Simulated Intermittent Contacts RISK ANALYSIS Julian, T. R., Canales, R. A., Leckie, J. O., Boehm, A. B. 2009; 29 (5): 617-632

    Abstract

    Existing microbial risk assessment models rarely incorporate detailed descriptions of human interaction with fomites. We develop a stochastic-mechanistic model of exposure to rotavirus from nondietary ingestion iterated by simulated intermittent fomes-mouth, hand-mouth, and hand-fomes contacts typical of a child under six years of age. This exposure is subsequently translated to risk using a simple static dose-response relationship. Through laboratory experiments, we quantified the mean rate of inactivation for MS2 phage on glass (0.0052/hr) and mean transfer between fingertips and glass (36%). Simulations using these parameters demonstrated that a child's ingested dose from a rotavirus-contaminated ball ranges from 2 to 1,000 virus over a period of one hour, with a median value of 42 virus. These results were heavily influenced by selected values of model parameters, most notably the concentration of rotavirus on fomes, frequency of fomes-mouth contacts, frequency of hand-mouth contacts, and virus transferred from fomes to mouth. The model demonstrated that mouthing of fomes is the primary exposure route, with hand mouthing contributions accounting for less than one-fifth of the child's dose over the first 10 minutes of interaction.

    View details for DOI 10.1111/j.1539-6924.2008.01193.x

    View details for Web of Science ID 000264892100002

    View details for PubMedID 19187484

  • Biogeographic Patterns in Genomic Diversity among a Large Collection of Vibrio cholerae Isolates APPLIED AND ENVIRONMENTAL MICROBIOLOGY Keymer, D. P., Lam, L. H., Boehm, A. B. 2009; 75 (6): 1658-1666

    Abstract

    Vibrio cholerae strains are capable of inhabiting multiple niches in the aquatic environment and in some cases cause disease in humans. However, the ecology and biodiversity of these bacteria in environmental settings remains poorly understood. We used the genomic fingerprinting technique enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR) to profile 835 environmental isolates from waters and sediments obtained at nine sites along the central California coast. We identified 115 ERIC-PCR genotypes from 998 fingerprints, with a reproducibility of 98.5% and a discriminatory power of 0.971. When the temporal dynamics at a subset of sampling sites were explored, several genotypes provided evidence for cosmopolitan or geographically restricted distributions, and other genotypes displayed nonrandom patterns of cooccurrence. Partial Mantel tests confirmed that genotypic similarity of isolates across all sampling events was correlated with environmental similarity (0.04 < or = r < or = 0.05), temporal proximity (r = 0.09), and geographic distance (r = 0.09). A neutral community model for all sampling events explained 61% of the variation in genotype abundance. Cooccurrence indices (C-score, C-board, and Combo) were significantly different than expected by chance, suggesting that the V. cholerae population may have a competitive structure, especially at the regional scale. Even though stochastic processes are undoubtedly important in generating biogeographic patterns in diversity, deterministic factors appear to play a significant, albeit small, role in shaping the V. cholerae population structure in this system.

    View details for DOI 10.1128/AEM.01304-08

    View details for Web of Science ID 000263920900024

    View details for PubMedID 19139224

  • A sea change ahead for recreational water quality criteria JOURNAL OF WATER AND HEALTH Boehm, A. B., Ashbolt, N. J., Colford, J. M., Dunbar, L. E., Fleming, L. E., Gold, M. A., Hansel, J. A., Hunter, P. R., Ichida, A. M., McGee, C. D., Soller, J. A., Weisberg, S. B. 2009; 7 (1): 9-20

    Abstract

    The United States Environmental Protection Agency is committed to developing new recreational water quality criteria for coastal waters by 2012 to provide increased protection to swimmers. We review the uncertainties and shortcomings of the current recreational water quality criteria, describe critical research needs for the development of new criteria, as well as recommend a path forward for new criteria development. We believe that among the most needed research needs are the completion of epidemiology studies in tropical waters and in waters adversely impacted by urban runoff and animal feces, as well as studies aimed to validate the use of models for indicator and pathogen concentration and health risk predictions.

    View details for DOI 10.2166/wh.2009.122

    View details for Web of Science ID 000264052900002

    View details for PubMedID 18957771

  • Growth of Enterococci in Unaltered, Unseeded Beach Sands Subjected to Tidal Wetting APPLIED AND ENVIRONMENTAL MICROBIOLOGY Yamahara, K. M., Walters, S. P., Boehm, A. B. 2009; 75 (6): 1517-1524

    Abstract

    Enterococci are indicator bacteria used to assess the risk of acquiring enteric disease from swimming in marine waters. Previous work identified beach sands as reservoirs of enterococci which can be transported from the sand to the sea, where they may instigate beach advisories. The present study establishes that naturally occurring enterococci can replicate in beach sands under environmentally relevant conditions. In unseeded, nonsterile microcosm experiments, it was shown that intermittent wetting of sands by seawater, like that which would occur at the high tide line, stimulates the transient replication of enterococci at rates of 0.20 to 0.63 per day (equivalent to doubling times of 1.1 to 3.5 days). Replication was not observed in control microcosms that were not subjected to wetting. Enterococci were enumerated using both culture-dependent (membrane filtration and mEI media) and culture-independent (quantitative PCR [QPCR], 23S rRNA gene based) techniques, which allowed tracking of both culturable and total enterococcus populations. Inhibition of QPCR and DNA extraction efficiencies were accounted for in the interpretation of the QPCR results. The results provide evidence that enterococci may not be an appropriate indicator of enteric disease risk at recreational beaches subject to nonpoint sources of pollution.

    View details for DOI 10.1128/AEM.02278-08

    View details for Web of Science ID 000263920900006

    View details for PubMedID 19151188

  • Sources of nutrients and fecal indicator bacteria to nearshore waters on the north shore of Kauai (Hawaii, USA) ESTUARIES AND COASTS Knee, K. L., Layton, B. A., Street, J. H., Boehm, A. B., Paytan, A. 2008; 31 (4): 607-622
  • Submarine discharge of nutrient-enriched fresh groundwater at Stinson Beach, California is enhanced during neap tides LIMNOLOGY AND OCEANOGRAPHY de Sieyes, N. R., Yamahara, K. M., Layton, B. A., Joyce, E. H., Boehm, A. B. 2008; 53 (4): 1434-1445
  • Fecal indicator bacteria and Salmonella in ponds managed as bird habitat, San Francisco Bay, California, USA WATER RESEARCH Shellenbarger, G. G., Athearn, N. D., Takekawa, J. Y., Boehm, A. B. 2008; 42 (12): 2921-2930

    Abstract

    Throughout the world, coastal resource managers are encouraging the restoration of previously modified coastal habitats back into wetlands and managed ponds for their ecosystem value. Because many coastal wetlands are adjacent to urban centers and waters used for human recreation, it is important to understand how wildlife can affect water quality. We measured fecal indicator bacteria (FIB) concentrations, presence/absence of Salmonella, bird abundance, and physico-chemical parameters in two coastal, managed ponds and adjacent sloughs for 4 weeks during the summer and winter in 2006. We characterized the microbial water quality in these waters relative to state water-quality standards and examined the relationship between FIB, bird abundance, and physico-chemical parameters. A box model approach was utilized to determine the net source or sink of FIB in the ponds during the study periods. FIB concentrations often exceeded state standards, particularly in the summer, and microbial water quality in the sloughs was generally lower than in ponds during both seasons. Specifically, the inflow of water from the sloughs to the ponds during the summer, more so than waterfowl use, appeared to increase the FIB concentrations in the ponds. The box model results suggested that the ponds served as net wetland sources and sinks for FIB, and high bird abundances in the winter likely contributed to net winter source terms for two of the three FIB in both ponds. Eight serovars of the human pathogen Salmonella were isolated from slough and pond waters, although the source of the pathogen to these wetlands was not identified. Thus, it appeared that factors other than bird abundance were most important in modulating FIB concentrations in these ponds.

    View details for DOI 10.1016/j.watres.2008.03.006

    View details for Web of Science ID 000257649100009

    View details for PubMedID 18457857

  • Shifts in the relative abundance of ammonia-oxidizing bacteria and archaea across physicochemical gradients in a subterranean estuary ENVIRONMENTAL MICROBIOLOGY Santoro, A. E., Francis, C. A., de Sieyes, N. R., Boehm, A. B. 2008; 10 (4): 1068-1079

    Abstract

    Submarine groundwater discharge to coastal waters can be a significant source of both contaminants and biologically limiting nutrients. Nitrogen cycling across steep gradients in salinity, oxygen and dissolved inorganic nitrogen in sandy 'subterranean estuaries' controls both the amount and form of nitrogen discharged to the coastal ocean. We determined the effect of these gradients on betaproteobacterial ammonia-oxidizing bacteria (beta-AOB) and ammonia-oxidizing archaea (AOA) in a subterranean estuary using the functional gene encoding ammonia monooxygenase subunit A (amoA). The abundance of beta-AOB was dramatically lower in the freshwater stations compared with saline stations, while AOA abundance remained nearly constant across the study site. This differing response to salinity altered the ratio of beta-AOB to AOA such that bacterial amoA was 30 times more abundant than crenarchaeal amoA at the oxic marine station, but nearly 10 times less abundant at the low-oxygen fresh and brackish stations. As the location of the brackish mixing zone within the aquifer shifted from landward in winter to oceanward in summer, the location of the transition from a beta-AOB-dominated to an AOA-dominated community also shifted, demonstrating the intimate link between microbial communities and coastal hydrology. Analysis of ammonia-oxidizing enrichment cultures at a range of salinities revealed that AOA persisted solely in the freshwater enrichments where they actively express amoA. Diversity (as measured by total richness) of crenarchaeal amoA was high at all stations and time points, in sharp contrast to betaproteobacterial amoA for which only two sequence types were found. These results offer new insights into the ecology of AOA and beta-AOB by elucidating conditions that may favour the numerical dominance of beta-AOB over AOA in coastal sediments.

    View details for DOI 10.1111/j.1462-2920.2007.01547.x

    View details for Web of Science ID 000254124100023

    View details for PubMedID 18266758

  • Enterococci concentrations in diverse coastal environments exhibit extreme variability ENVIRONMENTAL SCIENCE & TECHNOLOGY Boehm, A. B. 2007; 41 (24): 8227-8232

    Abstract

    Fecal indicator bacteria (FIB) concentrations in a single grab sample of water are used to notify the public about the safety of swimming in coastal waters. If concentrations are over a single-sample standard, waters are closed or placed under an advisory. Previous work has shown that notification errors occur often because FIB vary more quickly than monitoring results can be obtained (typically 24 h). Rapid detection technologies (such as quantitative polymerase chain reaction) that allow FIB quantification in hours have been suggested as a solution to notification errors. In the present study, I explore variability of enterococci (ENT) over time scales less than a day that might affect interpretation of FIB concentrations from a single grab sample, even if obtained rapidly. Five new data sets of ENT collected at 10 and 1 min periodicities for 24 and 1 h, respectively, are presented. Data sets are collected in diverse marine environments from a turbulent surf zone to a quiescent bay. ENT vary with solar and tidal cycles, as has been observed in previous studies. Over short time scales, ENT are extremely variable in each environment even the quiescent bay. Changes in ENT concentrations between consecutive samples (1 or 10 min apart) greater than the single-sample standard (104 most probable number per 100 mL) are not unusual. Variability, defined as the change in concentration between consecutive samples, is not distinct between environments. ENT change by 60% on average between consecutive samples, and by as much as 700%. Spectral analyses reveal no spectral peaks, but power-law decline of spectral density with frequency. Power-law exponents are close to 1 suggesting ENT time series share properties with 1/f noise and are fractal in nature. Since fractal time series have no characteristic time scale associated with them, it is not obvious how the fractal nature of ENT can be exploited for adaptive sampling or management. Policy makers, as well as scientists designing field campaigns for microbial source tracking and epidemiology studies, are cautioned that a single sample of water reveals little about the true water quality at a beach. Multiple samples must be taken to gain a snapshot into the patchy structure of microbial water quality and associated human health risk.

    View details for DOI 10.1021/es071807v

    View details for Web of Science ID 000251582800007

    View details for PubMedID 18200844

  • Frequent occurrence of the human-specific Bacteroides fecal marker at an open coast marine beach: relationship to waves, tides and traditional indicators ENVIRONMENTAL MICROBIOLOGY Santoro, A. E., Boehm, A. B. 2007; 9 (8): 2038-2049

    Abstract

    Molecular genetic markers, such as those from fecal Bacteroides microorganisms, can link microbial pollution with its source, and have been used successfully in studies of sheltered aquatic environments. Their applicability to wave-driven, open coast environments has not been tested. We assessed the contribution of a tidal outlet to surf zone water quality in coastal Orange County, California, USA by measuring three traditional culture-based fecal indicator bacteria (FIB) as well as the human-specific Bacteroides molecular marker (HF marker) at four shoreline locations. We found that total and fecal coliform levels were higher during low tides than high tides at two of the four stations, and that this effect was strongest at the mouth of the tidal lagoon and decayed with distance from the outlet. The HF marker was detected in 23% and 47% of samples from the tidal outlet and 26% and 41% of samples from an adjacent recreational beach in 2005 and 2006 respectively. Surprisingly, the station farthest from the tidal outlet had the highest occurrence of the HF marker. We found no relationship between FIB abundance and occurrence of the HF marker for individual samples, but that when the data were considered together by year, higher FIB abundance was correlated with a higher incidence of the HF marker. DNA sequences of the HF marker recovered from this site were > 99% similar to those recovered from other states and countries, suggesting low global diversity of this marker. These data provide strong support for the idea that multiple time points and physical conditions should be considered when assessing coastal water quality.

    View details for DOI 10.1111/j.1462-2920.2007.01319.x

    View details for Web of Science ID 000248451600014

    View details for PubMedID 17635548

  • Beach sands along the California coast are diffuse sources of fecal bacteria to coastal waters ENVIRONMENTAL SCIENCE & TECHNOLOGY Yamahara, K. M., Layton, B. A., Santoro, A. E., Boehm, A. B. 2007; 41 (13): 4515-4521

    Abstract

    Fecal indicator bacteria (FIB) are nearly ubiquitous in California (CA) beach sands. Sands were collected from 55 beaches along the CA coast. Ninety-one percent of the beaches had detectable enterococci (ENT) while 62% had detectable E. coli (EC) in their sands. The presence of a putative bacterial source (such as a river), the degree of wave shelter, and surrounding land use explained a significant (p < 0.05) fraction of the variation in both ENT and EC densities between beaches. Sand characteristics including moisture content, organic carbon, and percentfines, significantly (p < 0.05) influenced only EC densities in beach sand. We assayed 34 of 163 sand samples for salmonellae, but did not detect this bacterial pathogen. The potential for FIB to be transported from the sand to sea was investigated at a single wave-sheltered beach with high densities of ENT in beach sand: Lovers Point, CA (LP). We collected samples of exposed and submerged sands as well as water over a 24 h period in order to compare the disappearance or appearance of ENT in sand and the water column. Exposed sands had significantly higher densities of ENT than submerged sands with the highest densities located near the high tide line. Water column ENT densities began low, increased sharply during the first flood tide and slowly decreased over the remainder of the study. During the first flood tide, the number of ENT that entered the water column was nearly equivalent to the number of ENT lost from exposed sands when they were submerged by seawater. The decrease in nearshore ENT concentrations after the initial influx can be explained by ENT die-off and dilution with clean ocean water. While some ENT in the water and sand at LP might be of human origin because they were positive for the esp gene, others lacked the esp gene and were therefore equivocal with respect to their origin. Follow-up sampling at LP revealed the presence of the human specific Bacteroides marker in water and sand.

    View details for DOI 10.1021/es062822n

    View details for Web of Science ID 000247782500014

    View details for PubMedID 17695890

  • Detection and transformation of genome segments that differ within a coastal population of Vibrio cholerae strains APPLIED AND ENVIRONMENTAL MICROBIOLOGY Miller, M. C., Keymer, D. P., Avelar, A., Boehm, A. B., Schoolnik, G. K. 2007; 73 (11): 3695-3704

    Abstract

    Vibrio cholerae is an autochthonous member of diverse aquatic ecosystems around the globe. Collectively, the genomes of environmental V. cholerae strains comprise a large repository of encoded functions which can be acquired by individual V. cholerae lineages through uptake and recombination. To characterize the genomic diversity of environmental V. cholerae, we used comparative genome hybridization to study 41 environmental strains isolated from diverse habitats along the central California coast, a region free of endemic cholera. These data were used to classify genes of the epidemic V. cholerae O1 sequenced strain N16961 as conserved, variably present, or absent from the isolates. For the most part, absent genes were restricted to large mobile elements and have known functions in pathogenesis. Conversely, genes present in some, but not all, California isolates were in smaller contiguous clusters and were less likely to be near genes with functions in DNA mobility. Two such clusters of variable genes encoding different selectable metabolic phenotypes (mannose and diglucosamine utilization) were transformed into the genomes of environmental isolates by chitin-dependent competence, indicating that this mechanism of general genetic exchange is conserved among V. cholerae. The transformed DNA had an average size of 22.7 kbp, demonstrating that natural competence can mediate the movement of large chromosome fragments. Thus, whether variable genes arise through the acquisition of new sequences by horizontal gene transfer or by the loss of preexisting DNA though deletion, natural transformation provides a mechanism by which V. cholerae clones can gain access to the V. cholerae pan-genome.

    View details for DOI 10.1128/AEM.02735-06

    View details for Web of Science ID 000247016600029

    View details for PubMedID 17449699

  • Genomic and phenotypic diversity of coastal Vibrio cholerae strains is linked to environmental factors APPLIED AND ENVIRONMENTAL MICROBIOLOGY Keymer, D. P., Miller, M. C., Schoolnik, G. K., Boehm, A. B. 2007; 73 (11): 3705-3714

    Abstract

    Studies of Vibrio cholerae diversity have focused primarily on pathogenic isolates of the O1 and O139 serotypes. However, autochthonous environmental isolates of this species routinely display more extensive genetic diversity than the primarily clonal pathogenic strains. In this study, genomic and metabolic profiles of 41 non-O1/O139 environmental isolates from central California coastal waters and four clinical strains are used to characterize the core genome and metabolome of V. cholerae. Comparative genome hybridization using microarrays constructed from the fully sequenced V. cholerae O1 El Tor N16961 genome identified 2,787 core genes that approximated the projected species core genome within 1.6%. Core genes are almost universally present in strains with widely different niches, suggesting that these genes are essential for persistence in diverse aquatic environments. In contrast, the dispensable genes and phenotypic traits identified in this study should provide increased fitness for certain niche environments. Environmental parameters, measured in situ during sample collection, are correlated to the presence of specific dispensable genes and metabolic capabilities, including utilization of mannose, sialic acid, citrate, and chitosan oligosaccharides. These results identify gene content and metabolic pathways that are likely selected for in certain coastal environments and may influence V. cholerae population structure in aquatic environments.

    View details for DOI 10.1128/AEM.02736-06

    View details for Web of Science ID 000247016600030

    View details for PubMedID 17449702

  • Beach sands along the California coast are diffuse sources of fecal bacteria to coastal waters. Environmental Science & Technology Yamahara, K., M., Layton, B., A., Santoro, A., E., Boehm., A., B. 2007; 41: 4515-4521
  • Human development is linked to multiple water body impairments along the California coast ESTUARIES AND COASTS Handler, N. B., Payran, A., Higgins, C. P., Luthy, R. G., Boehm, A. B. 2006; 29 (5): 860-870
  • Regional public health cost estimates of contaminated coastal waters: A case study of gastroenteritis at southern california beaches ENVIRONMENTAL SCIENCE & TECHNOLOGY Given, S., Pendleton, L. H., Boehm, A. B. 2006; 40 (16): 4851-4858

    Abstract

    We present estimates of annual public health impacts, both illnesses and cost of illness, attributable to excess gastrointestinal illnesses caused by swimming in contaminated coastal waters at beaches in southern California. Beach-specific enterococci densities are used as inputs to two epidemiological dose-response models to predict the risk of gastrointestinal illness at 28 beaches spanning 160 km of coastline in Los Angeles and Orange Counties. We use attendance data along with the health cost of gastrointestinal illness to estimate the number of illnesses among swimmers and their likely economic impact. We estimate that between 627,800 and 1,479,200 excess gastrointestinal illnesses occur at beaches in Los Angeles and Orange Counties each year. Using a conservative health cost of gastroenteritis, this corresponds to an annual economic loss of dollars 21 or dollars 51 million depending upon the underlying epidemiological model used (in year 2000 dollars). Results demonstrate that improving coastal water quality could result in a reduction of gastrointestinal illnesses locally and a concurrent savings in expenditures on related health care costs.

    View details for DOI 10.1021/es060679s

    View details for Web of Science ID 000239684900012

    View details for PubMedID 16955877

  • Enterococci predictions from partial least squares regression models in conjunction with a single-sample standard improve the efficacy of beach management advisories ENVIRONMENTAL SCIENCE & TECHNOLOGY Hou, D., Rabinovici, S. J., Boehm, A. B. 2006; 40 (6): 1737-1743

    Abstract

    Beach health advisories are issued if enterococci (ENT) densities exceed the 30-d geometric mean or single-sample water quality criteria. Current ENT enumeration procedures require 1 day of incubation; therefore, beach managers make policy decisions using 1-day-old data. This is tantamount to using a model that assumes ENT density on day t is equal to ENT density on day t-1. Research has shown that ENT densities vary over time scales shorterthan a day, calling into question the usefulness of the current model for decision-making. We created Dynamic Partial Least Square Regression (DPLSR) models for ENT at water quality monitoring stations within two adjacent marine recreational sites, Huntington State Beach (HSB) and Huntington City (HCB) Beach, California, using publicly available environmental data and tested whether these models overcome the drawbacks of the current model. The DPLSR models provide a better prediction of ENT than the current models based on comparisons of root-mean-square errors of prediction and the numbers of type 1 and 2 errors. We compared outcomes in terms of predicted illness, swimmers deterred from entering the water, and net benefits to swimmers for hypothetical management scenarios where beach advisories were issued based on (a) the previously collected sample's ENT density in conjunction with the two water quality criteria, and (b) predictions from DPLSR models in conjunction with the single-sample standard. At both HSB and HCB the DPLSR scenario produced a more favorable balance between illness prevention and recreational access. The results call into question the current method of beach management and show that model-informed decision-making and elimination of the geometric mean standard will aid beach managers in achieving more favorable outcomes in terms of illness and access than are presently achieved using 1-day-old measurements, especially at beaches where water quality problems are chronic.

    View details for DOI 10.1021/es0515250

    View details for Web of Science ID 000236213900005

    View details for PubMedID 16570591

  • Composition and flux of groundwater from a California beach aquifer: Implications for nutrient supply to the surf zone (vol 26, pg 269, 2006) CONTINENTAL SHELF RESEARCH Boehm, A., Paytan, A., Shellenbarger, G. G., Davis, K. A. 2006; 26 (4): 554-554
  • Denitrifier community composition along a nitrate and salinity gradient in a coastal aquifer APPLIED AND ENVIRONMENTAL MICROBIOLOGY Santoro, A. E., Boehm, A. B., Francis, C. A. 2006; 72 (3): 2102-2109

    Abstract

    Nitrogen flux into the coastal environment via submarine groundwater discharge may be modulated by microbial processes such as denitrification, but the spatial scales at which microbial communities act and vary are not well understood. In this study, we examined the denitrifying community within the beach aquifer at Huntington Beach, California, where high-nitrate groundwater is a persistent feature. Nitrite reductase-encoding gene fragments (nirK and nirS), responsible for the key step in the denitrification pathway, were PCR amplified, cloned, and sequenced from DNAs extracted from aquifer sediments collected along a cross-shore transect, where groundwater ranged in salinity from 8 to 34 practical salinity units and in nitrate concentration from 0.5 to 330 muM. We found taxonomically rich and novel communities, with all nirK clones exhibiting <85% identity and nirS clones exhibiting <92% identity at the amino acid level to those of cultivated denitrifiers and other environmental clones in the database. Unique communities were found at each site, despite being located within 40 m of each other, suggesting that the spatial scale at which denitrifier diversity and community composition vary is small. Statistical analyses of nir sequences using the Monte Carlo-based program integral-Libshuff confirmed that some populations were indeed distinct, although further sequencing would be required to fully characterize the highly diverse denitrifying communities at this site.

    View details for DOI 10.1128/AEM.72.3.2102-2109.2006

    View details for Web of Science ID 000236069200045

    View details for PubMedID 16517659

  • Composition and flux of groundwater from a California beach aquifer: Implications for nutrient supply to the surf zone CONTINENTAL SHELF RESEARCH Boehm, A. B., Paytan, A., Shellenbarger, G. G., Davis, K. A. 2006; 26 (2): 269-282
  • An analytical model of enterococci inactivation, grazing, and transport in the surf zone of a marine beach WATER RESEARCH Boehm, A. B., Keymer, D. P., Shellenbarger, G. G. 2005; 39 (15): 3565-3578

    Abstract

    An analytical model of enterococci (ENT) concentrations in the surf zone of a long sandy beach is constructed considering the physical processes of dilution by rip currents and alongshore littoral drift, and the biological processes of inactivation and mortality by grazing. The solution is used to construct an expression for the length of shoreline adversely impacted by ENT from a point source. Two non-dimensional parameters are developed whose magnitude can be used to ascertain whether dilution, inactivation, or grazing is the dominant sink for ENT in the surf zone. The model is applied to beaches in southern California, USA. Model input parameters related to physical processes and inactivation are compiled from the literature. Laboratory experiments are conducted to determine grazing mortality rates of ENT (6.5 x 10(-6) s(-1)). Results indicate that at the field sites, between 1000 and 5000 m of shoreline are typically impacted by a continuous point source of ENT. Dilution is the primary cause of decline in ENT concentrations within the surf zone, with inactivation secondary and grazing tertiary. Results recommend strategic positioning of point sources and timing of effluent releases to take advantage of high dilution conditions. Our estimates for grazing mortality rates are within the same order of magnitude as some published inactivation rates, thus we cannot rule out the possibility that grazing is an important sink for ENT, especially in low dilution environments like enclosed bays.

    View details for Web of Science ID 000232417800014

    View details for PubMedID 16095656

  • Tidal forcing of enterococci at marine recreational beaches at fortnightly and semidiurnal frequencies ENVIRONMENTAL SCIENCE & TECHNOLOGY Boehm, A. B., Weisberg, S. B. 2005; 39 (15): 5575-5583

    Abstract

    Marine beach water quality is typically monitored in early morning once a week without respect to tidal condition. To assess the effect of tide on this public health warning system, we analyzed enterococci (ENT) data from 60 southern California marine beaches with differing geomorphology, orientation, and proximity to runoff sources. ENT concentrations during spring tides were significantly higher (p < 0.1) than those during neap tides at 50 of the beaches, and at the majority of these, water samples were also more than twice as likely to be out of compliance with the ENT single-sample standard during spring tides compared to neap tides. When tide range (spring/neap) and tide stage (ebb/flood) conditions were considered together, spring-ebb tides yielded the highest ENT concentrations and the greatest chance of exceeding the single-sample standard at the majority of beaches. The proximity to a terrestrial runoff source, the slope of the runoff source, the slope of the beach, and the orientation of the beach had minimal influence on the tidal modulation of ENT concentrations. The presence of spring and spring-ebb tide signals at such a great percentage of beaches suggests that tide should be considered in the design and interpretation of beach monitoring program data. It also suggests that ENT delivered by tidally forced sources other than terrestrial surficial runoff are widespread. Possibilities include ENT-laden groundwater (saline and fresh) from the beach aquifer as well as ENT-enriched sands, decaying wrack, and bird feces near the high water line.

    View details for DOI 10.1021/es048175m

    View details for Web of Science ID 000230919800020

    View details for PubMedID 16124289

  • Groundwater discharge: Potential association with fecal indicator bacteria in the surf zone ENVIRONMENTAL SCIENCE & TECHNOLOGY Boehm, A. B., Shellenbarger, G. G., Paytan, A. 2004; 38 (13): 3558-3566

    Abstract

    Short-lived radium isotopes (223Ra and 224Ra) are used to investigate the potential association between groundwater discharge and microbial pollution at Huntington Beach, CA. We establish the tidally driven exchange of groundwater from the surficial beach aquifer across the beach face. Groundwater is found to be a source of nutrients (silica, inorganic nitrogen, and orthophosphate) to the surf zone, and these nutrients could possibly provide an environment for enhanced growth or increased persistence of fecal indicator bacteria (FIB). Ammonium and ortho-phosphate explain up to 12-20% of the variance in FIB levels in the surf zone. Elevated levels of FIB were only found in 1 of the 26 groundwater samples. However, FIB in the surf zone covary with radium at fortnightly, diurnal, and semi-diurnal tidal periods. In addition, radium accounts for up to 38% of the variance in log-FIB levels in the surf zone. A column experiment illustrates that Enterococcus suspended in Huntington Beach saline groundwater is not significantly filtered by sand collected from the field. This work establishes a mechanism for the subterranean delivery of FIB pollution to the surf zone from the surficial aquifer and presents evidence that supports an association between groundwater discharge and FIB.

    View details for DOI 10.1021/es035385a

    View details for Web of Science ID 000222396400021

    View details for PubMedID 15296305

  • Scaling and management of fecal indicator bacteria in runoff from a coastal urban watershed in southern California ENVIRONMENTAL SCIENCE & TECHNOLOGY Reeves, R. L., Grant, S. B., Mrse, R. D., Oancea, C. M., Sanders, B. F., Boehm, A. B. 2004; 38 (9): 2637-2648

    Abstract

    This paper describes a series of field studies aimed at identifying the spatial distribution and flow forcing of fecal indicator bacteria in dry and wet weather runoff from the Talbert watershed, a highly urbanized coastal watershed in southern California. Runoff from this watershed drains through tidal channels to a popular public beach, Huntington State Beach, which has experienced chronic surf zone water quality problems over the past several years. During dry weather, concentrations of fecal indicator bacteria are highest in inland urban runoff, intermediate in tidal channels harboring variable mixtures of urban runoff and ocean water, and lowest in ocean water at the base of the watershed. This inland-to-coastal gradient is consistent with the hypothesis that urban runoff from the watershed contributes to coastal pollution. On a year round basis, the vast majority (>99%) of fecal indicator bacteria loading occurs during storm events when runoff diversions, the management approach of choice, are not operating. During storms, the load of fecal indicator bacteria in runoff follows a power law of the form L approximately Qn, where L is the loading rate (in units of fecal indicator bacteria per time), Q is the volumetric flow rate (in units of volume per time), and the exponent n ranges from 1 to 1.5. This power law and the observed range of exponent values are consistent with the predictions of a mathematical model that assumes fecal indicator bacteria in storm runoff originate from the erosion of contaminated sediments in drainage channels or storm sewers. The theoretical analysis, which is based on a conventional model for the shear-induced erosion of particles from land and channel-bed surfaces, predicts that the magnitude of the exponent n reflects the geometry of the stormwater conveyance system from which the pollution derives. This raises the possibility that the scaling properties of pollutants in stormwater runoff (i.e., the value of n) may harbor information about the origin of nonpoint source pollution.

    View details for Web of Science ID 000221189900029

    View details for PubMedID 15180060

  • Covariation of coastal water temperature and microbial pollution at interannual to tidal periods GEOPHYSICAL RESEARCH LETTERS Boehm, A. B., Lluch-Cota, D. B., Davis, K. A., Winant, C. D., Monismith, S. G. 2004; 31 (6)
  • Sources, management, and scaling of fecal indicator bacteria in runoff from a coastal urban watershed in Southern California. Environmental Science and Technology Reeves, R., L., Grant, S., B., Mrse, R., D., Oancea, C., M. C., Sanders, B., F., Boehm., A., B. 2004; 38: 2637-2648
  • Bacterial Contamination and Submarine Groundwater Discharge-A Possible Link ENVIRONMENTAL CHEMISTRY Paytan, A., Boehm, A. B., Shellenbarger, G. G. 2004; 1 (1): 29-30

    View details for DOI 10.1071/EN04002

    View details for Web of Science ID 000207050400009

  • Model of microbial transport and inactivation in the surf zone and application to field measurements of total coliform in Northern Orange County, California ENVIRONMENTAL SCIENCE & TECHNOLOGY Boehm, A. B. 2003; 37 (24): 5511-5517

    Abstract

    The classic model of pollutant transport in the surf zone of a long, sandy beach developed by Inman et al. (J. Geophys. Res. 1971, 76, 3493) is altered to account for first-order pollutant inactivation in an effort to understand how rip cell dilution and bacterial inactivation control the length of shoreline adversely impacted by microbial pollution from a point source. A dimensionless number gamma dictates whether physical processes (dilution of microbes in the surf zone by rip cell mixing) or biological processes (microbial inactivation) control the distribution of pollution along the shoreline. Estimates of gamma for beaches in Northern Orange County, California, indicate that dilution is the primary factor controlling total coliform levels surrounding two drains that release nuisance runoff directly onto the beach. It is also shown that, even when alongshore currents are fast, pollutant levels will drop e-fold at distances under 4000 m from the point source due to dilution alone. Because dilution is ultimately controlled by wave climate and shoreline morphology, the results suggest the strategic position of drains and other point sources in high dilution wave environments will reduce potential adverse effects on beach water quality. In addition, the results stress the importance of understanding hydrodynamics when conducting microbial source tracking at wave-dominated marine beaches.

    View details for DOI 10.1021/es034321x

    View details for Web of Science ID 000187248000006

    View details for PubMedID 14717158

  • Tiered approach for identification of a human fecal pollution source at a recreational beach: Case study at Avalon Cay, Catalina Island, California ENVIRONMENTAL SCIENCE & TECHNOLOGY Boehm, A. B., Fuhrman, J. A., Mrse, R. D., Grant, S. B. 2003; 37 (4): 673-680

    Abstract

    Recreational marine beaches in California are posted as unfit for swimming when the concentration of fecal indicator bacteria (FIB) exceeds any of seven concentration standards. Finding and mitigating sources of shoreline FIB is complicated by the many potential human and nonhuman sources of these organisms and the complex fate and transport processes that control their concentrations. In this study, a three-tiered approach is used to identify human and nonhuman sources of FIB in Avalon Bay, a popular resort community on Catalina Island in southern California. The first and second tiers utilize standard FIB tests to spatially isolate the FIB signal, to characterize the variability of FIB over a range of temporal scales, and to measure FIB concentrations in potential sources of these organisms. In the third tier, water samples from FIB "hot spots" and sources are tested for human-specific bacteria Bacteroides/Prevotella and enterovirus to determine whether the FIB are from human sewage or from nonhuman sources such as bird feces. FIB in Avalon Bay appear to be from multiple, primarily land-based, sources including bird droppings, contaminated subsurface water, leaking drains, and runoff from street wash-down actvities. Multiple shoreline samples and two subsurface water samples tested positive for human-specific bacteria and enterovirus, suggesting that at least a portion of the FIB contamination is from human sewage.

    View details for DOI 10.1021/es025934x

    View details for Web of Science ID 000181067100003

    View details for PubMedID 12636264

  • A model of microbial transport and inactivation in the surf zone and application to field measurements of total coliform in Northern Orange County, California. Environmental Science and Technology Boehm., A., B. 2003; 37: 5511-5517
  • A tiered approach for identification of a human fecal pollution source at a recreational beach: Case study at Avalon Bay, Catalina Island, California, USA. Environmental Science and Technology Boehm., A., B., Fuhrman, J., A., Mrse, R., D., Grant., S., B. 2003; 37: 673-680
  • A scaling theory for number-flux distributions generated during steady-state coagulation and settling and application to particles in Lake Zurich, Switzerland JOURNAL OF COLLOID AND INTERFACE SCIENCE Boehm, A. B. 2002; 254 (2): 266-273

    Abstract

    In this study, we extend the established scaling theory for cluster size distributions generated during unsteady coagulation to number-flux distributions that arise during steady-state coagulation and settling in an unmixed water mass. The scaling theory predicts self-similar number-flux distributions and power-law decay of total number flux with depth. The shape of the number-flux distributions and the power-law exponent describing the decay of the total number flux are shown to depend on the homogeneity and small i/j limit of the coagulation kernel and the exponent kappa, which describes the variation in settling velocity with cluster volume. Particle field measurements from Lake Zurich, collected by U. Weilenmann and co-workers (Limnol. Oceanogr.34, 1 (1989)), are used to illustrate how the scaling predictions can be applied to a natural system. This effort indicates that within the mid-depth region of Lake Zurich, clusters of the same size preferentially interact and large clusters react with one another more quickly than small ones, indicative of clusters coagulating in a reaction-limited regime.

    View details for DOI 10.1006/jcis.2002.8599

    View details for Web of Science ID 000178935400009

    View details for PubMedID 12702397

  • Decadal and shorter period variability of surf zone water quality at Huntington Beach, California. Environmental Science and Technology Boehm., A., B., Grant, S., B., Kim, J., H., Mowbray, S., L., McGee, C., D., Clark, C., D. 2002; 36: 3885-3892
  • Cross-shelf transport at Huntington Beach -Implications for the fate of sewage discharged through an offshore ocean outfall. Environmental Science and Technology Boehm., A., B., Sanders, B., F., Winant., C., D. 2002; 36: 1899-1906
  • A steady-state model of particulate organic carbon flux below the mixed layer and application to the Joint Global Ocean Flux Study. Journal of Geophysical Research-Oceans Boehm, A., B., Grant., S., B. 2001; 106: 31227-21237
  • Generation of enterococci bacteria in a coastal saltwater marsh and its impact on surf zone water quality. Environmental Science & Technology Grant, S., B., Sanders, B., F., Boehm, A., B., Redman, J., A., Kim, J., H., Mrse, R., D. 2001; 35: 2407-2416
  • Particle coagulation and the memory of initial conditions Journal of Physics A: Mathematics and General Boehm, A., B., Poor, C., Grant., S., B. 1998; 31: 9241-9254
  • The influence of coagulation, sedimentation, and grazing by zooplankton on phytoplankton aggregate size distributions in aquatic systems. Journal of Geophysical Research-Oceans Boehm, A., B., Grant., S., B. 1998; 103: 15601-15612

Books and Book Chapters


  • Marine and Freshwater Fecal Indicators and Source Identification. Encyclopedia of Sustainability Science and Technology McLellan, S., L., Boehm, A., B., Shanks, O., C. edited by Grimes, D., J. 2012
  • Case Studies: Beach Environments. Microbial Source Tracking: Methods, Applications, and Case Studies Solo-Gabriele, H., M., Boehm, A., B., Scott, T., M., Sinigalliano, C. edited by Hagedorn, C., Blanch, A., Harwood, J. Springer. 2011
  • Recreational Water risk: Pathogens and Fecal Indicators. Encyclopedia of Sustainability Science and Technology Boehm, A., B., Soller, J., A. edited by Meyers, R., A. Springer. 2011
  • Oceans and human health. Encyclopedia of Environmental Health Boehm, A., B., Bischel, H., N. edited by Nriagu, J. Burlington, Elsevier.. 2011: 223-230
  • Modeling Fate and Transport of Fecal Bacteria in Surface Water. The Fecal Indicator Bacteria Nevers, M., N., Boehm, A., B. edited by Sadowsky, M., Whitman, R. ASM Press. 2010: 328
  • Classical and Molecular Methods to Measure Fecal Bacteria. The Fecal Indicator Bacteria Edge, T., A., Boehm, A., B. edited by Sadowsky, M., Whitman, R. ASM Press. 2010: 328
  • Now-casting recreational water quality. Statistical Framework for Water Quality Criteria and Monitoring Boehm, A., B., Whitman, R., L., Nevers, M., B., Hou, D., Weisberg, S., B. edited by Wymer, L., Dufour, A. 2007