Stanford Advisors

All Publications

  • Rapid assessment of changes in phage bioactivity using dynamic light scattering. bioRxiv : the preprint server for biology Dharmaraj, T., Kratochvil, M. J., Pourtois, J. D., Chen, Q., Hajfathalian, M., Hargil, A., Lin, Y. H., Evans, Z., Oromí-Bosch, A., Berry, J. D., McBride, R., Haddock, N. L., Holman, D. R., van Belleghem, J. D., Chang, T. H., Barr, J. J., Lavigne, R., Heilshorn, S. C., Blankenberg, F. G., Bollyky, P. L. 2023


    Extensive efforts are underway to develop bacteriophages as therapies against antibiotic-resistant bacteria. However, these efforts are confounded by the instability of phage preparations and a lack of suitable tools to assess active phage concentrations over time. Here, we use Dynamic Light Scattering (DLS) to measure changes in phage physical state in response to environmental factors and time, finding that phages tend to decay and form aggregates and that the degree of aggregation can be used to predict phage bioactivity. We then use DLS to optimize phage storage conditions for phages from human clinical trials, predict bioactivity in 50-year-old archival stocks, and evaluate phage samples for use in a phage therapy/wound infection model. We also provide a web-application (Phage-ELF) to facilitate DLS studies of phages. We conclude that DLS provides a rapid, convenient, and non-destructive tool for quality control of phage preparations in academic and commercial settings.

    View details for DOI 10.1101/2023.07.02.547396

    View details for PubMedID 37425882

    View details for PubMedCentralID PMC10327207

  • Bacteriophage and Bacterial Susceptibility, Resistance, and Tolerance to Antibiotics. Pharmaceutics Chen, Q., Dharmaraj, T., Cai, P. C., Burgener, E. B., Haddock, N. L., Spakowitz, A. J., Bollyky, P. L. 2022; 14 (7)


    Bacteriophages, viruses that infect and replicate within bacteria, impact bacterial responses to antibiotics in complex ways. Recent studies using lytic bacteriophages to treat bacterial infections (phage therapy) demonstrate that phages can promote susceptibility to chemical antibiotics and that phage/antibiotic synergy is possible. However, both lytic and lysogenic bacteriophages can contribute to antimicrobial resistance. In particular, some phages mediate the horizontal transfer of antibiotic resistance genes between bacteria via transduction and other mechanisms. In addition, chronic infection filamentous phages can promote antimicrobial tolerance, the ability of bacteria to persist in the face of antibiotics. In particular, filamentous phages serve as structural elements in bacterial biofilms and prevent the penetration of antibiotics. Over time, these contributions to antibiotic tolerance favor the selection of resistance clones. Here, we review recent insights into bacteriophage contributions to antibiotic susceptibility, resistance, and tolerance. We discuss the mechanisms involved in these effects and address their impact on bacterial fitness.

    View details for DOI 10.3390/pharmaceutics14071425

    View details for PubMedID 35890320

  • Filamentous bacteriophage delays healing of Pseudomonas-infected wounds. Cell reports. Medicine Bach, M. S., de Vries, C. R., Khosravi, A., Sweere, J. M., Popescu, M. C., Chen, Q., Demirdjian, S., Hargil, A., Van Belleghem, J. D., Kaber, G., Hajfathalian, M., Burgener, E. B., Liu, D., Tran, Q., Dharmaraj, T., Birukova, M., Sunkari, V., Balaji, S., Ghosh, N., Mathew-Steiner, S. S., El Masry, M. S., Keswani, S. G., Banaei, N., Nedelec, L., Sen, C. K., Chandra, V., Secor, P. R., Suh, G. A., Bollyky, P. L. 2022; 3 (6): 100656


    Chronic wounds infected by Pseudomonas aeruginosa (Pa) are characterized by disease progression and increased mortality. We reveal Pf, a bacteriophage produced by Pa that delays healing of chronically infected wounds in human subjects and animal models of disease. Interestingly, impairment of wound closure by Pf is independent of its effects on Pa pathogenesis. Rather, Pf impedes keratinocyte migration, which is essential for wound healing, through direct inhibition of CXCL1 signaling. In support of these findings, a prospective cohort study of 36 human patients with chronic Pa wound infections reveals that wounds infected with Pf-positive strains of Pa are more likely to progress in size compared with wounds infected with Pf-negative strains. Together, these data implicate Pf phage in the delayed wound healing associated with Pa infection through direct manipulation of mammalian cells. These findings suggest Pf may have potential as a biomarker and therapeutic target in chronic wounds.

    View details for DOI 10.1016/j.xcrm.2022.100656

    View details for PubMedID 35732145

  • Filamentous Bacteriophage Delay Healing Of Pseudomonas-Infected Wounds Khosravi, A., Bach, M. S., de Vries, C. R., Sweere, J. M., Popescu, M., Chen, Q., Hargil, A., Van Belleghem, J. D., Kaber, G., Burgener, E. B., Liu, D., Quynh-Lam Tran, Dharmaraj, T., Sunkari, V., Balaji, S., Ghosh, N., Mathew-Steiner, S. S., Keswani, S. G., Banaei, N., Nedelec, L., Sen, C. K., Chandra, V., Secor, P. R., Suh, G., Bollyky, P. WILEY. 2022: A27
  • A Filamentous Bacteriophage Protein Inhibits Type IV Pili To Prevent Superinfection of Pseudomonas aeruginosa. mBio Schmidt, A. K., Fitzpatrick, A. D., Schwartzkopf, C. M., Faith, D. R., Jennings, L. K., Coluccio, A., Hunt, D. J., Michaels, L. A., Hargil, A., Chen, Q., Bollyky, P. L., Dorward, D. W., Wachter, J., Rosa, P. A., Maxwell, K. L., Secor, P. R. 1800: e0244121


    Pseudomonas aeruginosa is an opportunistic pathogen that causes infections in a variety of settings. Many P. aeruginosa isolates are infected by filamentous Pf bacteriophage integrated into the bacterial chromosome as a prophage. Pf virions can be produced without lysing P. aeruginosa. However, cell lysis can occur during superinfection, which occurs when Pf virions successfully infect a host lysogenized by a Pf prophage. Temperate phages typically encode superinfection exclusion mechanisms to prevent host lysis by virions of the same or similar species. In this study, we sought to elucidate the superinfection exclusion mechanism of Pf phage. Initially, we observed that P. aeruginosa that survive Pf superinfection are transiently resistant to Pf-induced plaquing and are deficient in twitching motility, which is mediated by type IV pili (T4P). Pf utilize T4P as a cell surface receptor, suggesting that T4P are suppressed in bacteria that survive superinfection. We tested the hypothesis that a Pf-encoded protein suppresses T4P to mediate superinfection exclusion by expressing Pf proteins in P. aeruginosa and measuring plaquing and twitching motility. We found that the Pf protein PA0721, which we termed Pf superinfection exclusion (PfsE), promoted resistance to Pf infection and suppressed twitching motility by binding the T4P protein PilC. Because T4P play key roles in biofilm formation and virulence, the ability of Pf phage to modulate T4P via PfsE has implications in the ability of P. aeruginosa to persist at sites of infection. IMPORTANCE Pf bacteriophage (phage) are filamentous viruses that infect Pseudomonas aeruginosa and enhance its virulence potential. Pf virions can lyse and kill P. aeruginosa through superinfection, which occurs when an already infected cell is infected by the same or similar phage. Here, we show that a small, highly conserved Pf phage protein (PA0721, PfsE) provides resistance to superinfection by phages that use the type IV pilus as a cell surface receptor. PfsE does this by inhibiting assembly of the type IV pilus via an interaction with PilC. As the type IV pilus plays important roles in virulence, the ability of Pf phage to modulate its assembly has implications for P. aeruginosa pathogenesis.

    View details for DOI 10.1128/mbio.02441-21

    View details for PubMedID 35038902

  • A Filamentous Bacteriophage Protein Inhibits Type IV Pili To Prevent Superinfection of Pseudomonas aeruginosa MBIO Schmidt, A. K., Fitzpatrick, A. D., Schwartzkopf, C. M., Faith, D. R., Jennings, L. K., Coluccio, A., Hunt, D. J., Michaels, L. A., Hargil, A., Chen, Q., Bollyky, P. L., Dorward, D. W., Wachter, J., Rosa, P. A., Maxwell, K. L., Secor, P. R. 2022; 13 (1)
  • The Safety and Toxicity of Phage Therapy: A Review of Animal and Clinical Studies. Viruses Liu, D., Van Belleghem, J. D., de Vries, C. R., Burgener, E., Chen, Q., Manasherob, R., Aronson, J. R., Amanatullah, D. F., Tamma, P. D., Suh, G. A. 2021; 13 (7)


    Increasing rates of infection by antibiotic resistant bacteria have led to a resurgence of interest in bacteriophage (phage) therapy. Several phage therapy studies in animals and humans have been completed over the last two decades. We conducted a systematic review of safety and toxicity data associated with phage therapy in both animals and humans reported in English language publications from 2008-2021. Overall, 69 publications met our eligibility criteria including 20 animal studies, 35 clinical case reports or case series, and 14 clinical trials. After summarizing safety and toxicity data from these publications, we discuss potential approaches to optimize safety and toxicity monitoring with the therapeutic use of phage moving forward. In our systematic review of the literature, we found some adverse events associated with phage therapy, but serious events were extremely rare. Comprehensive and standardized reporting of potential toxicities associated with phage therapy has generally been lacking in the published literature. Structured safety and tolerability endpoints are necessary when phages are administered as anti-infective therapeutics.

    View details for DOI 10.3390/v13071268

    View details for PubMedID 34209836

  • Filamentous Bacteriophages and the Competitive Interaction between Pseudomonas aeruginosa Strains under Antibiotic Treatment: a Modeling Study. mSystems Pourtois, J. D., Kratochvil, M. J., Chen, Q., Haddock, N. L., Burgener, E. B., De Leo, G. A., Bollyky, P. L. 2021: e0019321


    Pseudomonas aeruginosa (Pa) is a major bacterial pathogen responsible for chronic lung infections in cystic fibrosis patients. Recent work has implicated Pf bacteriophages, nonlytic filamentous viruses produced by Pa, in the chronicity and severity of Pa infections. Pf phages act as structural elements in Pa biofilms and sequester aerosolized antibiotics, thereby contributing to antibiotic tolerance. Consistent with a selective advantage in this setting, the prevalence of Pf-positive (Pf+) bacteria increases over time in these patients. However, the production of Pf phages comes at a metabolic cost to bacteria, such that Pf+ strains grow more slowly than Pf-negative (Pf-) strains in vitro. Here, we use a mathematical model to investigate how these competing pressures might influence the relative abundance of Pf+ versus Pf- strains in different settings. Our model suggests that Pf+ strains of Pa cannot outcompete Pf- strains if the benefits of phage production falls onto both Pf+ and Pf- strains for a majority of parameter combinations. Further, phage production leads to a net positive gain in fitness only at antibiotic concentrations slightly above the MIC (i.e., concentrations for which the benefits of antibiotic sequestration outweigh the metabolic cost of phage production) but which are not lethal for Pf+ strains. As a result, our model suggests that frequent administration of intermediate doses of antibiotics with low decay rates and high killing rates favors Pf+ over Pf- strains. These models inform our understanding of the ecology of Pf phages and suggest potential treatment strategies for Pf+ Pa infections. IMPORTANCE Filamentous phages are a frontier in bacterial pathogenesis, but the impact of these phages on bacterial fitness is unclear. In particular, Pf phages produced by Pa promote antibiotic tolerance but are metabolically expensive to produce, suggesting that competing pressures may influence the prevalence of Pf+ versus Pf- strains of Pa in different settings. Our results identify conditions likely to favor Pf+ strains and thus antibiotic tolerance. This study contributes to a better understanding of the unique ecology of filamentous phages in both environmental and clinical settings and may facilitate improved treatment strategies for combating antibiotic tolerance.

    View details for DOI 10.1128/mSystems.00193-21

    View details for PubMedID 34156288

  • N-Acetyl cysteine abrogates silver-induced reactive oxygen species in human cells without altering silver-based antimicrobial activity TOXICOLOGY LETTERS Shah, K. N., Shah, P. N., Mullen, A. R., Chen, Q., Southerland, M. R., Chirra, B., DeBerardinis, R. J., Cannon, C. L. 2020; 332: 118–29


    Silver-based antimicrobials are widely used topically to treat infections associated with multi-drug resistant (MDR) pathogens. Expanding this topical use to aerosols to treat lung infections requires understanding and preventing silver toxicity in the respiratory tract. A key mechanism resulting in silver-induced toxicity is the production of reactive oxygen species (ROS). In this study, we have verified ROS generation in silver-treated bronchial epithelial cells prompting evaluation of three antioxidants, N-acetyl cysteine (NAC), ascorbic acid, and melatonin, to identify potential prophylactic agents. Among them, NAC was the only candidate that abrogated the ROS generation in response to silver acetate exposure resulting in the rescue of these cells from silver-associated toxicity. Further, this protective effect directly translated to preservation of metabolic activity, as demonstrated by the normal levels of citric acid cycle metabolites in NAC-pretreated silver acetate-exposed cells. Because the citric acid cycle remained functional, silver-exposed cells pre-incubated with NAC demonstrated significantly higher levels of adenosine triphosphate levels compared with NAC-free controls. Moreover, we found that this prodigious capacity of NAC to rescue silver acetate-exposed cells was due not only to its antioxidant activity, but also to its ability to directly bind silver. Despite binding to silver, NAC did not alter the antimicrobial activity of silver acetate.

    View details for DOI 10.1016/j.toxlet.2020.07.014

    View details for Web of Science ID 000566774200002

    View details for PubMedID 32659471

  • Phages in vaccine design and immunity; mechanisms and mysteries. Current opinion in biotechnology de Vries, C. R., Chen, Q. n., Demirdjian, S. n., Kaber, G. n., Khosravi, A. n., Liu, D. n., Van Belleghem, J. D., Bollyky, P. L. 2020; 68: 160–65


    Bacteriophages have attracted extensive interest in vaccine design. This includes the use of phage display technology to select antigens, the use of engineered phages displaying target antigens in vaccine formulations, and phage DNA vaccines. However, the development of these approaches is limited in part by uncertainty regarding the underlying mechanisms by which phages elicit immunity. This has stymied the clinical development of this technology. Here we review the immunology of phage vaccines and highlight the gaps in our knowledge regarding the underlying mechanisms. First, we review the basic biology of phages and their use in vaccines. Next we discuss what is known about the mechanisms of immunity against engineered phages and phage DNA. Finally, we highlight the gaps in our understanding regarding the immunogenicity of these preparations. We argue that mechanistic insight into the immunology of phage vaccines is essential for the further development and clinical utility of these technologies.

    View details for DOI 10.1016/j.copbio.2020.11.002

    View details for PubMedID 33316575

  • Pf Bacteriophage and Their Impact on Pseudomonas Virulence, Mammalian Immunity, and Chronic Infections. Frontiers in immunology Secor, P. R., Burgener, E. B., Kinnersley, M. n., Jennings, L. K., Roman-Cruz, V. n., Popescu, M. n., Van Belleghem, J. D., Haddock, N. n., Copeland, C. n., Michaels, L. A., de Vries, C. R., Chen, Q. n., Pourtois, J. n., Wheeler, T. J., Milla, C. E., Bollyky, P. L. 2020; 11: 244


    Pf bacteriophage are temperate phages that infect the bacterium Pseudomonas aeruginosa, a major cause of chronic lung infections in cystic fibrosis (CF) and other settings. Pf and other temperate phages have evolved complex, mutualistic relationships with their bacterial hosts that impact both bacterial phenotypes and chronic infection. We and others have reported that Pf phages are a virulence factor that promote the pathogenesis of P. aeruginosa infections in animal models and are associated with worse skin and lung infections in humans. Here we review the biology of Pf phage and what is known about its contributions to pathogenesis and clinical disease. First, we review the structure, genetics, and epidemiology of Pf phage. Next, we address the diverse and surprising ways that Pf phages contribute to P. aeruginosa phenotypes including effects on biofilm formation, antibiotic resistance, and motility. Then, we cover data indicating that Pf phages suppress mammalian immunity at sites of bacterial infection. Finally, we discuss recent literature implicating Pf in chronic P. aeruginosa infections in CF and other settings. Together, these reports suggest that Pf bacteriophage have direct effects on P. aeruginosa infections and that temperate phages are an exciting frontier in microbiology, immunology, and human health.

    View details for DOI 10.3389/fimmu.2020.00244

    View details for PubMedID 32153575

    View details for PubMedCentralID PMC7047154

  • Pyoverdine-Dependent Virulence of Pseudomonas aeruginosa Isolates From Cystic Fibrosis Patients FRONTIERS IN MICROBIOLOGY Kang, D., Revtovich, A., Chen, Q., Shah, K. N., Cannon, C. L., Kirienko, N. 2019; 10: 2048


    The development of therapies that modulate or prevent pathogen virulence may be a key strategy for circumventing antimicrobial resistance. Toward that end, we examined the production of pyoverdine, a key virulence determinant, in ∼70 Pseudomonas aeruginosa isolates from pediatric cystic fibrosis patients. Pyoverdine production was heterogeneous and showed a clear correlation with pathogenicity in Caenorhabditis elegans and an acute murine pneumonia model. Examination showed pyoverdine accumulation in host tissues, including extrapharyngeal tissues of C. elegans and lung tissues of mice, where accumulation correlated with host death. Many of the isolates tested were resistant to multiple antimicrobials, so we assayed the ability of pyoverdine inhibitors to mitigate virulence and rescue pyoverdine-mediated host pathology. Representatives from three different classes of pyoverdine inhibitors (gallium, fluoropyrimidines, and LK11) significantly improved survival. Our findings highlight the utility of targeting virulence factors in general, and pyoverdine in particular, as a promising method to control bacterial pathogenesis as the utility of antimicrobials continues to diminish.

    View details for DOI 10.3389/fmicb.2019.02048

    View details for Web of Science ID 000484517100001

    View details for PubMedID 31551982

    View details for PubMedCentralID PMC6743535

  • Minocycline and Silver Dual-Loaded Polyphosphoester-Based Nanoparticles for Treatment of Resistant Pseudomonas aeruginosa MOLECULAR PHARMACEUTICS Chen, Q., Shah, K. N., Zhang, F., Salazar, A. J., Shah, P. N., Li, R., Sacchettini, J. C., Wooley, K. L., Cannon, C. L. 2019; 16 (4): 1606–19


    Pseudomonas aeruginosa has been detected in the lungs of ∼50% of patients with cystic fibrosis (CF), including 20% of adult CF patients. The majority of these adult patients harbor multi-drug resistant (MDR) strains, limiting the available treatment options. Silver has long been used as a broad-spectrum antimicrobial agent with a low incidence of resistance. Despite low toxicity, poor availability of silver cations mandates a high dosage to effectively eradicate infections. To address this shortcoming of silver, nanoparticles have been used as delivery devices to improve treatment outcomes. Furthermore, studies have demonstrated that synergistic combinations with careful dose calibrations and efficient delivery systems result in superior antimicrobial activity while avoiding potential side effects of both therapeutics. Here 4-epi-minocycline, a metabolite of minocycline, was identified as an active antimicrobial against P. aeruginosa using a high-throughput screen. The antimicrobial activities of 4-epi-minocycline, minocycline, and silver acetate against clinical isolates of P. aeruginosa obtained from CF patients were evaluated in vitro. Next, the synergistic activity of the silver/minocycline combination against P. aeruginosa isolates was investigated using checkerboard assays and identified with end-point colony forming unit determination assays. Finally, nanoparticles coloaded with minocycline and silver were evaluated in vitro for antimicrobial activity. The results demonstrated that both silver and minocycline are potent antimicrobials alone and that the combination allows a reduced dosage of both therapeutics to achieve the same antimicrobial effect. Furthermore, the proposed synergistic silver/minocycline combination can be coloaded into nanoparticles as a next-generation antibiotic to combat the threats presented by MDR pathogens.

    View details for DOI 10.1021/acs.molpharmaceut.8b01288

    View details for Web of Science ID 000463462300019

    View details for PubMedID 30817887

  • Antimicrobial Activity of Ibuprofen against Cystic Fibrosis-Associated Gram-Negative Pathogens ANTIMICROBIAL AGENTS AND CHEMOTHERAPY Shah, P. N., Marshall-Batty, K. R., Smolen, J. A., Tagaev, J. A., Chen, Q., Rodesney, C. A., Le, H. H., Gordon, V. D., Greenberg, D. E., Cannon, C. L. 2018; 62 (3)


    Clinical trials have demonstrated the benefits of ibuprofen therapy in cystic fibrosis (CF) patients, an effect that is currently attributed to ibuprofen's anti-inflammatory properties. Yet, a few previous reports demonstrated an antimicrobial activity of ibuprofen as well, although none investigated its direct effects on the pathogens found in the CF lung, which is the focus of this work. Determination of ibuprofen's in vitro antimicrobial activity against Pseudomonas aeruginosa and Burkholderia species strains through measurements of the endpoint number of CFU and growth kinetics showed that ibuprofen reduced the growth rate and bacterial burden of the tested strains in a dose-dependent fashion. In an in vitroPseudomonas biofilm model, a reduction in the rate of biomass accumulation over 8 h of growth with ibuprofen treatment was observed. Next, an acute Pseudomonas pneumonia model was used to test this antimicrobial activity after the oral delivery of ibuprofen. Following intranasal inoculation, ibuprofen-treated mice exhibited lower CFU counts and improved survival compared with the control animals. Preliminary biodistribution studies performed after the delivery of ibuprofen to mice by aerosol demonstrated a rapid accumulation of ibuprofen in serum and minimum retention in lung tissue and bronchoalveolar lavage fluid. Therefore, ibuprofen-encapsulated polymeric nanoparticles (Ibu-NPs) were formulated to improve the pharmacokinetic profile. Ibu-NPs formulated for aerosol delivery inhibited the growth of P. aeruginosa in vitro and may provide a convenient dosing method. These results provide an additional explanation for the previously observed therapeutic effects of ibuprofen in CF patients and further strengthen the argument for its use by these patients.

    View details for DOI 10.1128/AAC.01574-17

    View details for Web of Science ID 000427121800055

    View details for PubMedID 29311081

    View details for PubMedCentralID PMC5826130