Equol neutralizes toxin B to combat Clostridioides difficile infection without disrupting the gut microbiota.

Clostridioides difficile (C. difficile) toxin B (TcdB) is essential for C. difficile pathogenicity. TcdB induces apoptosis in host cells by internalizing and utilizing its glycosyltransferase activity to modify members of the small GTPase protein family through glycosylation. The intestinal environment is critical for the colonization of C. difficile, and the use of broad-spectrum antibiotics disrupts the balance of the gut microbiota, leading to increased susceptibility of the host to C. difficile. At present, the mainstream clinical approach for treating C. difficile infection (CDI) involves antibiotic therapies such as vancomycin, which disrupt the gut microbiota and are associated with a considerable risk of infection recurrence. Therefore, there is an urgent clinical need to develop new strategies to combat CDI. Here, we have identified a natural compound, equol, which inhibits the TcdB-mediated glycosylation of Rac1 through direct interaction, thereby reducing TcdB-induced cell death. Equol functions as an inhibitor of indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO), effectively suppressing the conversion of tryptophan to kynurenine in the intestinal tract while preserving the integrity of the gut microbiota. Concurrently, equol exhibits robust antioxidant properties, which markedly reduced TcdB-mediated oxidative damage and subsequent cell death. These findings suggest that equol holds therapeutic potential for the treatment of CDI.