A new study published in Gut explored the role of bile acid metabolism in the effectiveness of faecal microbiota transplantation (FMT) to treat recurrent Clostridium difficile infection (rCDI). Stool samples from patients with rCDI before FMT contained reduced proportions of bacterial species that produce bile salt hydrolases (BSHs) compared with samples collected after FMT. Furthermore, pre-FMT samples contained increased levels of the C. difficile germinant taurocholic acid, which negatively correlated with BSH-producing bacterial genera. Following FMT, copy numbers of BSH genes and BSH activity recovered. In vitro studies showed that BSH-mediated hydrolysis of taurocholic acid effectively suppressed C. difficile germination. In addition, C. difficile viable counts in a mouse model of rCDI were reduced by ~70% after administration of Escherichia coli engineered to express highly active BSH.