Factors that Affect Clostridioides Difficile Infections Using In Vivo and In Vitro Approaches

Abstract

C. difficile a Gram-positive, spore-forming, pathogenic bacterium, is the leading cause of nosocomial-associated diarrhea in the United States. C. difficile is characterized as an urgent threat by the Centers for Disease Control and Prevention (CDC) due to its emerging antibiotic resistance and increased community spread. Although secondary bile acids and CDI are strongly and negatively correlated in humans and in animal models of disease a, causative role for secondary bile acid protection against CDI has not been established. We found that bacteria that can perform 7α-dehydroxylation to generate secondary bile acids, protect against C. difficile infections even in the absence of secondary bile acid generation. Furthermore, using a CYP8b1-\- (cholic acid-deficient) mouse strain, we show that deoxycholate (a major secondary bile salt) is not required for protection against CDI. Instead, we provide evidence that the consumption of amino acids that are important for Stickland metabolism by protective strains, may deplete nutrients needed by the C. difficile bacterium during host colonization. Although some of our data shows that secondary bile acids are not the mechanism by which colonic microbiota protect against CDI, we also show that C. difficile cells can “seed” an environment with cholate so that other bacterial species produce deoxycholate. This production stimulates C. difficile to generate a biofilm. These results emphasize the complex interactions taking place between C. difficile and the gut microbiome. The work described in this dissertation highlights the importance of microbe-microbe interaction and suggest that C. difficile can interact with bile acids to, potentially, maintain itself in the GI.