Parabacteroides distasonis alleviates Clostridioides difficile infection in mice while modulating secondary bile acids.

Clostridioides difficile infection (CDI) is a major cause of antibiotic-associated diarrhea, with frequent recurrences closely linked to antibiotic-induced dysbiosis of the gut microbiota and bile acid metabolism. Parabacteroides distasonis, a potential probiotic capable of converting primary to secondary bile acids, has shown therapeutic promise in several metabolic and inflammatory diseases. This study evaluated the preventive and therapeutic effects of P. distasonis against CDI and explored the underlying mechanisms. We characterized the probiotic properties of four P. distasonis strains and investigated the inhibitory activity of strain 1190003 against C. difficile, as well as its protective and therapeutic efficacy in mouse models. Gut microbiota structure and bile acid metabolic profiles were analyzed by integrating 16S rRNA gene sequencing and metabolomics. The four P. distasonis strains exhibited strong acid and bile salt tolerance as well as auto-aggregation ability. Supernatants from P. distasonis co-cultured with cholic acid (4 mM and 8 mM) significantly inhibited C. difficile growth, toxin expression and spore formation, with deoxycholic acid identified as the key inhibitory metabolite. Both live P. distasonis and its culture supernatant alleviated disease severity in CDI mouse models and ameliorated gut microbiota dysbiosis. Notably, the relative abundance of Parabacteroides goldsteinii was increased following supernatant treatment. Furthermore, intervention with either live P. distasonis or its supernatant elevated the level of hyodeoxycholic acid. In summary, P. distasonis acts as a potential probiotic that alleviates CDI by ameliorating gut microbiota dysbiosis and remodeling bile acid metabolism. These findings provide experimental evidence for its use as a microbiota-based therapeutic strategy.