Bacteriophages as Modulators of Bacterial Colonization

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PROJECT SUMMARY Multidrug-resistant organisms (MDROs) remain major causes of morbidity and mortality in hematopoietic cell transplant (HCT) recipients. Because of the substantial use of antibiotics in these patients, their gut microbiome balance is perturbed and becomes dominated by MDROs, vancomycin-resistant enterococci (VRE) in particular. This disturbance is associated with subsequent invasive infections such as bacteremia that can lead to fatal outcome. Restoration of the normal balance of the gut flora and reduction or control of MDRO colonization may curtail these complications and improve outcomes. One innovative approach to restore the microbiome balance of the gut flora and reduce colonization with MDROs in HCT recipients is the administration of bacteriophages (i.e., phages). Phages are ubiquitous and natural entities, present in the environment and in our bodies, and capable of lysing specific pathogens without disturbing the host’s normal flora while averting the collateral damage of antimicrobial usage. My long-term research goal is to understand how phages contribute to host-microbe interactions and their overall impact on the health of HCT recipients. Our preliminary data indicate that VRE colonization can cause inflammation in the gut of germ-free wild-type mice. Additionally, we found that phages are present in high numbers in HCT patients’ stool samples and that VRE phages can be recovered from environmental samples and can lyse a variety of VRE strains in a larva model. The objective of the proposed research is to investigate the interactions between phages, the gut bacterial microbiome, and host responses in VRE-colonized HCT recipients and to identify biomarkers in the gut phage population predisposing patients to complications such as bacterial infections or graft versus host disease. The central hypothesis for this project is that VRE phages can restore balance in the gut microbiota by reducing inflammation and VRE colonization in HCT recipients. My ultimate goal is to generate significant findings and new hypotheses for an R01 application aiming at (1) optimizing the design of a chemotherapy- treated bone marrow-reconstituted mouse model mimicking the condition of HCT patients, (2) testing the efficacy of phages and phages+antibiotic synergy in preventing major MDRO infections in this mouse model, and (3) validating the role of certain phage populations in predicting and preventing poor outcomes. The rationale is that this line of work will provide supportive evidence for future development and evaluation of a phage-based intervention in humans. My long-term career goal is to become a leading investigator with expertise in the design of effective and safe phage-based natural therapeutic products that may restore a healthy gut microbiota and curtail serious complications encountered in HCT recipients (i.e., MDROs), thus improving their overall health outcomes. The proposal will aid in the fight against MDROs by curtailing the incidence of MDRO colonization and infections and by improving survival and quality-of-life of HCT recipients.