The pathogenesis of Clostridioides difficile infection (CDI), and mechanisms of efficacy of faecal microbiota transplant (FMT) in treating recurrent CDI (rCDI), remain poorly-understood. Certain bile acids affect the ability of C. difficile to undergo germination or vegetative growth. Loss of gut microbiota-derived bile-metabolising enzymes may
predispose to CDI via perturbation of bile metabolism, and restitution of gut bile-metabolising functionality could mediate FMT’s efficacy. Initially, human samples were analysed, i.e.: 1) biofluids collected from rCDI patients pre- and post-FMT (and their donors), and 2) stool samples from primary CDI patients, including both
recurrers and non-recurrers. Analysis included: 16S rRNA gene sequencing; liquid chromatography-mass spectrometry for bile acid profiling; gas chromatography-mass spectrometry for short chain fatty acid (SCFA) quantification; bile salt hydrolase (BSH) enzyme activity; and qPCR of bsh/ baiCD genes involved in bile metabolism. Human results were validated in C. difficile batch cultures and a rCDI mouse model. A reduced proportion of the stool microbiota of rCDI patients pre-FMT contained BSH-producing bacteria compared to donors or post-FMT. Pre-FMT stool was enriched in
taurocholic acid (TCA; a potent trigger to C. difficile germination); TCA levels negatively correlated with bacterial genera containing BSH-producing organisms. Post-FMT stool demonstrated recovered BSH activity and microbial bsh/ baiCD gene copy number compared with pre-treatment (p<0.05), and recovery of SCFA including valerate (p<0.001).
Dynamics of stool bile acids/ BSH activity differed in primary CDI patients with and without disease
recurrence. In batch cultures, culture supernatant from engineered bsh-expressing E. coli reduced TCA-mediated C. difficile germination relative to supernatant from BSH-negative E. coli. C. difficile total viable counts were ~70% reduced in a rCDI mouse model after administration of BSH-expressing E. coli relative to mice receiving BSH-negative E. coli (p<0.05). These data demonstrate that gut microbiota BSH functionality is a key mechanism influencing vulnerability to CDI and efficacy of FMT.