Background:  Clostridium difficile infection (CDI) is a major cause of  hospital-acquired diarrhea. Secondary bile acids were shown to confer  resistance to colonization by C. difficile. 7α-dehydroxylation is a key  step in transformation of primary to secondary bile acids and required  genes have been located in a single bile acid-inducible (bai) operon in  C. scindens as well as in C. hiranonis, two Clostridium sp. recently  reported to protect against C. difficile colonization.

Aim: To analyze baiCD gene abundance in C. difficile positive and negative fecal samples.

Material & methods: A species-specific qPCR for detecting baiCD genes was established.  Fecal samples of patients with CDI, asymptomatic toxigenic C. difficile  colonization (TCD), non-toxigenic C. difficile colonization (NTCD), of  C. difficile negative (NC) patients, and of two patients before and  after fecal microbiota transplantation (FMT) for recurrent CDI (rCDI)  were tested for the presence of the baiCD genes.

Results: The prevalence of the baiCD gene cluster was significantly higher  in C. difficile negative fecal samples than in samples of patients  diagnosed with CDI (72.5% (100/138) vs. 35.9% (23/64; p<0.0001). No  differences in baiCD gene cluster prevalence were seen between NC and  NTCD or NC and TCD samples. Both rCDI patients were baiCD-negative at  baseline, but one of the two patients turned positive after successful  FMT from a baiCD-positive donor.

Conclusion: Fecal samples of CDI patients are less frequently baiCD-positive  than samples from asymptomatic carriers or C. difficile-negative  individuals. Furthermore, we present a case of baiCD positivity observed  after successful FMT for rCDI.

Conflict of interest statement

Competing Interests: M.J.G.T.  Vehreschild is a consultant to: Berlin Chemie, MSD/Merck and Astellas  Pharma; has served at the speakers’ bureau of: Astellas Pharma, Basilea,  Gilead Sciences, Merck/MSD, Organobalance and Pfizer; received research  funding from: 3M, Astellas Pharma, DaVolterra, Gilead Sciences,  Merck/MSD, Morphochem, Organobalance, and Seres Therapeutics. O.  Bachmann served as a consultant for Astellas Pharma, and received  speaker’s fees from MSD. This does not alter our adherence to PLOS ONE  policies on sharing data and materials.