Bifidobacteria antagonize the life cycle of Clostridioides difficile.

Clostridioides difficile is a spore-forming pathogen capable of causing severe disease in humans. Critical stages in the biological cycle of this microorganism include sporogenesis/germination and toxin production by vegetative cells. Antagonizing these pivotal events could aid in prevention and treatment to manage this pathogen. Given that bifidobacteria can impede the growth, toxin production, and in vivo effects of C. difficile, the present study aimed to determine the impact of selected strains of bifidobacteria on crucial steps of the pathogen's biological cycle. Clinical strains of C. difficile, including ALCD3, GCD2, GCD4, and the reference strain VPI 10463 (ATCC 43255), were utilized. Bifidobacteria strains comprised CIDCA 5310 and CIDCA 5317 (Bifidobacterium bifidum and Bifidobacterium adolescentis, respectively). Cocultures of bifidobacteria with C. difficile resulted in a strain-dependent inhibition of sporulation (thermoresistant forms). This effect could be partially attributed to the production of lactic acid. Co-cultivation with all three bifidobacteria downregulated the expression of the tcdB gene, whereas strains CIDCA 5310 and CIDCA 5317, but not CIDCA 531, downregulated the expression of the cspAB gene. Bifidobacteria were capable of deconjugating taurocholate, as demonstrated by the increase in cholic acid concentration. Remarkably, strain CIDCA 531 almost entirely reduced taurocholate concentration. This ability correlated with the inhibitory effect on germination of spent culture supernatants of bifidobacterial cultures grown in medium containing taurocholate. Our results demonstrate that bifidobacteria can modify the biological cycle of C. difficile by altering the efficiency of sporulation and germination. Additionally, co-cultivation with bifidobacteria modulates the expression of genes associated with toxins and critical events in sporogenesis. These findings are significant for understanding the underlying mechanisms of the probiotic effect of bifidobacteria in the context of C. difficile infections.