Taken together, our data indicate that, despite secondary bile acid production by a healthy microbiota being a useful biomarker for colonization resistance against C. difficile [12,26,31], secondary bile acid production and downstream FXR-FGF19 signaling does not appear to be the primary mechanism by which the microbiota protect the host against C. difficile colonization and infection. This evidence concerns the gene FGF19 and infection.