Defining the role of enterococci in reshaping Clostridioides difficile infection - SUMMARY 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 microbial ecosystem and complex metabolic environment during invasion of the gastrointestinal tract. Thus, the study of pathogen-microbiota interactions during infection is central to our understanding of susceptibility to, severity of, and treatment of enteric infections. One of the most significant enteric pathogens globally is Clostridioides difficile. C. difficile is a spore-forming bacterium that causes a wide range of gastrointestinal (GI) disorders varying in severity from mild diarrhea to fulminant colitis and/or death. Over the past decade, incidence, severity, and costs associated with C. difficile infection (CDI) have increased dramatically; however, the factors that govern this broad spectrum of disease remain unknown. The primary risk factor for CDI is antibiotic treatment, which reduces colonization resistance to C. difficile by disrupting the resident microbial community inhabiting the GI tract. Surprisingly, little is known about how C. difficile cooperates with the rich collection of microorganisms in the GI tract. Moreover, we still understand very little about the impact of microenvironments and distinct metabolic niches on CDI. The studies proposed in this application will provide a molecular blueprint of CDI through the application of advanced imaging mass spectrometry and provide in-depth mechanistic insights into the role of the microbiota in shaping C. difficile virulence. Our preliminary studies demonstrate that a group of opportunistic pathogens, the enterococci, dramatically remodel the metabolic environment in the CDI gut and are a source of amino acids for C. difficile energy production. Enterococcus-mediated metabolic shaping of the gut metabolome enhances C. difficile colonization and support fitness following disease manifestation. Based on these fundamental discoveries, we propose a series of studies aimed at understanding the role enterococci play in CDI and defining the molecular mechanisms of interspecies interactions during infection. Completion of this work will (i) define the impact of enterococci on the metabolic environment during CDI and (ii) determine molecular mechanisms of enterococcal-mediated control of C. difficile virulence. Together, this work will define the supportive role that pathogenic microbiota play in the outcome of CDI and shed light on the importance of integration of metabolic signals from the microbiota in pathogen virulence.
