All Publications

  • 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

  • Leishmania donovani infection suppresses Allograft Inflammatory Factor-1 in monocytes and macrophages to inhibit inflammatory responses. Scientific reports da Silva, R. L., Elizondo, D. M., Brandy, N. Z., Haddock, N. L., Boddie, T. A., de Oliveira, L. L., de Jesus, A. R., de Almeida, R. P., de Moura, T. R., Lipscomb, M. W. 2021; 11 (1): 946


    Macrophages and monocytes are important for clearance of Leishmania infections. However, immune evasion tactics employed by the parasite results in suppressed inflammatory responses, marked by deficient macrophage functions and increased accumulation of monocytes. This results in an ineffective ability to clear parasite loads. Allograft Inflammatory Factor-1 (AIF1) is expressed in myeloid cells and serves to promote immune responses. However, AIF1 involvement in monocyte and macrophage functions during parasitic infections has not been explored. This study now shows that Leishmania donovani inhibits AIF1 expression in macrophages to block pro-inflammatory responses. Mice challenged with the parasite had markedly reduced AIF1 expression in splenic macrophages. Follow-up studies using in vitro approaches confirmed that L. donovani infection in macrophages suppresses AIF1 expression, which correlated with reduction in pro-inflammatory cytokine production and increased parasite load. Ectopic overexpression of AIF1 in macrophages provided protection from infection, marked by robust pro-inflammatory cytokine production and efficient pathogen clearance. Further investigations found that inhibiting AIF1 expression in bone marrow cells or monocytes impaired differentiation into functional macrophages. Collectively, results show that AIF1 is a critical regulatory component governing monocyte and macrophage immune functions and that L. donovani infection can suppress the gene as an immune evasion tactic.

    View details for DOI 10.1038/s41598-020-79068-6

    View details for PubMedID 33441583

  • 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

  • Hyaluronan synthesis inhibition impairs antigen presentation and delays transplantation rejection. Matrix biology : journal of the International Society for Matrix Biology Marshall, P. L., Nagy, N. n., Kaber, G. n., Barlow, G. L., Ramesh, A. n., Xie, B. J., Linde, M. H., Haddock, N. L., Lester, C. A., Tran, Q. L., de Vries, C. n., Hargil, A. n., Malkovskiy, A. n., Gurevich, I. n., Martinez, H. A., Kuipers, H. F., Yadava, K. n., Zhang, X. n., Evanko, S. P., Gebe, J. A., Wang, X. n., Vernon, R. B., de la Motte, C. n., Wight, T. N., Engleman, E. G., Krams, S. M., Meyer, E. n., Bollyky, P. L. 2020


    A coat of pericellular hyaluronan surrounds mature dendritic cells (DC) and contributes to cell-cell interactions. We asked whether 4-methylumbelliferone (4MU), an oral inhibitor of HA synthesis, could inhibit antigen presentation. We find that 4MU treatment reduces pericellular hyaluronan, destabilizes interactions between DC and T-cells, and prevents T-cell proliferation in vitro and in vivo. These effects were observed only when 4MU was added prior to initial antigen presentation but not later, consistent with 4MU-mediated inhibition of de novo antigenic responses. Building on these findings, we find that 4MU delays rejection of allogeneic pancreatic islet transplant and allogeneic cardiac transplants in mice and suppresses allogeneic T-cell activation in human mixed lymphocyte reactions. We conclude that 4MU, an approved drug, may have benefit as an adjunctive agent to delay transplantation rejection.

    View details for DOI 10.1016/j.matbio.2020.12.001

    View details for PubMedID 33290836

  • 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

  • Allograft Inflammatory Factor-1 Governs Hematopoietic Stem Cell Differentiation Into cDC1 and Monocyte-Derived Dendritic Cells Through IRF8 and RelB in vitro. Frontiers in immunology Elizondo, D. M., Brandy, N. Z., da Silva, R. L., Haddock, N. L., Kacsinta, A. D., de Moura, T. R., Lipscomb, M. W. 2019; 10: 173


    The multistep differentiation process from hematopoietic stem cells through common myeloid progenitors into committed dendritic cell (DC) subsets remains to be fully addressed. These studies now show that Allograft Inflammatory Factor-1 (AIF1) is required for differentiation of classical DC type 1 (cDC1) subsets and monocyte-derived DC (Mo-DC). Phenotypic studies found that AIF1 expression increased in committed subsets differentiating from common myeloid progenitors (CMP). However, silencing AIF1 expression in hematopoietic stem progenitors restrained the capacity to differentiate into Mo-DC and cDC1 cell subsets under GM-CSF or Flt3-L stimuli conditions, respectively. This was further marked by restrained expression of IRF8, which is critical for development of Mo-DC and cDC1 subsets. As a result, absence of AIF1 restrained the cells at the Lin-CD117+FcγR-CD34+ CMP stage. Further biochemical studies revealed that abrogating AIF1 resulted in inhibition of the NFκB family member RelB expression and p38 MAPK phosphorylation during differentiation of Mo-DC. Lastly, protein binding studies identified that AIF1 interacts with protein kinase C (PKC) to influence downstream signaling pathways. Taken together, this is the first report showing a novel role of AIF1 as a calcium-responsive scaffold protein that supports IRF8 expression and interacts with PKC to drive NFκB-related RelB for successfully differentiating hematopoietic progenitor cells into cDC and Mo-DC subsets under Flt3-L and GM-CSF stimuli, respectively.

    View details for DOI 10.3389/fimmu.2019.00173

    View details for PubMedID 30800127

    View details for PubMedCentralID PMC6375893

  • Drebrin 1 in dendritic cells regulates phagocytosis and cell surface receptor expression through recycling for efficient antigen presentation IMMUNOLOGY Elizondo, D. M., Andargie, T. E., Haddock, N. L., Boddie, T. A., Lipscomb, M. W. 2019; 156 (2): 136–46


    Phagocytosis, macropinocytosis and antigen presentation by dendritic cells (DC) requires reorganization of the actin cytoskeleton. Drebrin (Dbn1) is an actin binding and stabilizing protein with roles in endocytosis, formation of dendrite spines in neurons and coordinating cell-cell synapses in immune cells. However, its role in DC phagocytosis and antigen presentation is unknown. These studies now report that silencing of Dbn1 in DC resulted in restrained cell surface display of receptors, most notably MHC class I and II and co-stimulatory molecules. This, as expected, resulted in impaired antigen-specific T-cell activation and proliferation. Studies additionally revealed that knockdown of Dbn1 in DC impaired macropinocytosis and phagocytosis. However, there was a concomitant increase in fluid-phase uptake, suggesting that Dbn1 is responsible for the differential control of macropinocytosis versus micropinocytosis activities. Taken together, these findings now reveal that Dbn1 plays a major role in coordinating the actin cytoskeletal activities responsible for antigen presentation in DC.

    View details for DOI 10.1111/imm.13010

    View details for Web of Science ID 000455609300005

    View details for PubMedID 30317558

    View details for PubMedCentralID PMC6328995

  • Filamentous bacteriophages are associated with chronic Pseudomonas lung infections and antibiotic resistance in cystic fibrosis. Science translational medicine Burgener, E. B., Sweere, J. M., Bach, M. S., Secor, P. R., Haddock, N. n., Jennings, L. K., Marvig, R. L., Johansen, H. K., Rossi, E. n., Cao, X. n., Tian, L. n., Nedelec, L. n., Molin, S. n., Bollyky, P. L., Milla, C. E. 2019; 11 (488)


    Filamentous bacteriophage (Pf phage) contribute to the virulence of Pseudomonas aeruginosa infections in animal models, but their relevance to human disease is unclear. We sought to interrogate the prevalence and clinical relevance of Pf phage in patients with cystic fibrosis (CF) using sputum samples from two well-characterized patient cohorts. Bacterial genomic analysis in a Danish longitudinal cohort of 34 patients with CF revealed that 26.5% (n = 9) were consistently Pf phage positive. In the second cohort, a prospective cross-sectional cohort of 58 patients with CF at Stanford, sputum qPCR analysis showed that 36.2% (n = 21) of patients were Pf phage positive. In both cohorts, patients positive for Pf phage were older, and in the Stanford CF cohort, patients positive for Pf phage were more likely to have chronic P. aeruginosa infection and had greater declines in pulmonary function during exacerbations than patients negative for Pf phage presence in the sputum. Last, P. aeruginosa strains carrying Pf phage exhibited increased resistance to antipseudomonal antibiotics. Mechanistically, in vitro analysis showed that Pf phage sequesters these same antibiotics, suggesting that this mechanism may thereby contribute to the selection of antibiotic resistance over time. These data provide evidence that Pf phage may contribute to clinical outcomes in P. aeruginosa infection in CF.

    View details for PubMedID 30996083

  • IL-10 producing CD8(+) CD122(+) PD-1(+) regulatory T cells are expanded by dendritic cells silenced for Allograft Inflammatory Factor-1 JOURNAL OF LEUKOCYTE BIOLOGY Elizondo, D. M., Andargie, T. E., Haddock, N. L., Louzada da Silva, R. L., de Moura, T., Lipscomb, M. W. 2019; 105 (1): 123–30


    Allograft Inflammatory Factor-1 (AIF1) is a cytoplasmic scaffold protein that contains Ca2+ binding EF-hand and PDZ interaction domains important for mediating intracellular signaling complexes in immune cells. The protein plays a dominant role in both macrophage- and dendritic cell (DC)-mediated inflammatory responses. This study now reports that AIF1 expression in DC is important in directing CD8+ T cell effector responses. Silencing AIF1 expression in murine CD11c+ DC suppressed antigen-specific CD8+ T cell activation, marked by reduced CXCR3, IFNγ and Granzyme B expression, and restrained proliferation. These primed CD8+ T cells had impaired cytotoxic killing of target cells in vitro. In turn, studies identified that AIF1 silencing in DC robustly expanded IL-10 producing CD8+ CD122+ PD-1+ regulatory T cells that suppressed neighboring immune effector responses through both IL-10 and PD-1-dependent mechanisms. In vivo studies recapitulated bystander suppression of antigen-responsive CD4+ T cells by the CD8+ Tregs expanded from the AIF1 silenced DC. These studies further demonstrate that AIF1 expression in DC serves as a potent governor of cognate T cell responses and present a novel target for engineering tolerogenic DC-based immunotherapies.

    View details for DOI 10.1002/JLB.1A0118-010RR

    View details for Web of Science ID 000454409400012

    View details for PubMedID 30512224

    View details for PubMedCentralID PMC6310075