Bile acid-independent protection against Clostridioides difficile infection

Clostridioides difficile infections occur upon ecological / metabolic disruptions to the normal colonic microbiota, commonly due to broad-spectrum antibiotic use. Metabolism of bile acids through a 7 alpha-dehydroxylation pathway found in select members of the healthy microbiota is regarded to be the protective mechanism by which C. difficile is excluded. These 7 alpha-dehydroxylated secondary bile acids are highly toxic to C. difficile vegetative growth, and antibiotic treatment abolishes the bacteria that perform this metabolism. However, the data that supports the hypothesis that secondary bile acids protect against C. difficile infection is supported only by in vitro data and correlative studies. Here we show that bacteria that 7 alpha-dehydroxylate primary bile acids protect against C. difficile infection in a bile acid-independent manner. We monoassociated germ-free, wildtype or Cyp8b1(-/-) (cholic acid-deficient) mutant mice and infected them with C. difficile spores. We show that 7 alpha-dehydroxylation (i.e., secondary bile acid generation) is dispensable for protection against C. difficile infection and provide evidence that Stickland metabolism by these organisms consumes nutrients essential for C. difficile growth. Our findings indicate secondary bile acid production by the microbiome is a useful biomarker for a C. difficile-resistant environment but the microbiome protects against C. difficile infection in bile acid-independent mechanisms.

Automated summary

Infections of Clostridioides difficile result from disruptions to the normal colonic microbiota, often caused by broad-spectrum antibiotics. While secondary bile acids are toxic to C. difficile, their generation through 7 alpha-dehydroxylation is not necessary for protection against C. difficile infection. Instead, bacteria that 7 alpha-dehydroxylate primary bile acids protect against C. difficile through bile acid-independent mechanisms, suggesting that Stickland metabolism plays a key role in consuming essential nutrients for C. difficile growth.