Defining the role of enterococci in reshaping Clostridioides difficile infection

Our understanding of pathogen virulence has largely been established by studying organisms in isolation.However enteric infections are polymicrobial by nature as pathogens become exposed to a rich microbialecosystem and complex metabolic environment during invasion of the gastrointestinal tract. Thus the study ofpathogen-microbiota interactions during infection is central to our understanding of susceptibility to severity ofand treatment of enteric infections. One of the most significant enteric pathogens globally is Clostridioidesdifficile. C. difficile is a spore-forming bacterium that causes a wide range of gastrointestinal (GI) disordersvarying in severity from mild diarrhea to fulminant colitis and/or death. Over the past decade incidence severityand costs associated with C. difficile infection (CDI) have increased dramatically; however the factors thatgovern this broad spectrum of disease remain unknown. The primary risk factor for CDI is antibiotic treatmentwhich reduces colonization resistance to C. difficile by disrupting the resident microbial community inhabiting theGI tract. Surprisingly little is known about how C. difficile cooperates with the rich collection of microorganismsin the GI tract. Moreover we still understand very little about the impact of microenvironments and distinctmetabolic niches on CDI. The studies proposed in this application will provide a molecular blueprint of CDIthrough the application of advanced imaging mass spectrometry and provide in-depth mechanistic insights intothe role of the microbiota in shaping C. difficile virulence. Our preliminary studies demonstrate that a group ofopportunistic pathogens the enterococci dramatically remodel the metabolic environment in the CDI gut andare a source of amino acids for C. difficile energy production. Enterococcus-mediated metabolic shaping of thegut metabolome enhances C. difficile colonization and support fitness following disease manifestation. Basedon these fundamental discoveries we propose a series of studies aimed at understanding the role enterococciplay in CDI and defining the molecular mechanisms of interspecies interactions during infection. Completion ofthis work will (i) define the impact of enterococci on the metabolic environment during CDI and (ii) determinemolecular mechanisms of enterococcal-mediated control of C. difficile virulence. Together this work will definethe supportive role that pathogenic microbiota play in the outcome of CDI and shed light on the importance ofintegration of metabolic signals from the microbiota in pathogen virulence.