Intestinal bile acids directly modulate the structure and function of C. difficile TcdB toxin

Significance Clostridioides difficile is a bacterial pathogen of global importance that is a major cause of hospital-acquired diarrhea. Antibiotic-mediated disruptions to the gut microbiota and associated metabolome promoteC. difficile growth and infection through mechanisms that are poorly understood. Here, we show that intestinal bile acids, which are known to play a role inC. difficile germination and outgrowth, also directly bind and inhibit TcdB toxin, the primary virulence determinant ofC. difficile . Bile acid binding induces a major conformational change in TcdB structure that prevents receptor binding and uptake into cells. In addition to suggesting a role for bile acids in protecting againstC. difficile pathogenesis, these findings highlight an approach to blockC. difficile virulence.