Toxin A/B (TcdA; TcdB)

Toxin A (TcdA) and Toxin B (TcdB) are large clostridial glucosylating toxins produced by *Clostridioides difficile*, a bacterial pathogen responsible for severe antibiotic-associated diarrhea and colitis. Both toxins are AB-type exotoxins, consisting of an enzymatic "A" subunit (N-terminal glucosyltransferase domain) and a "B" subunit (delivery domain with receptor-binding, pore-forming, and autoprotease domains). Upon binding host cell receptors and internalization, the toxins translocate their glucosyltransferase domain into the cytosol, where they inactivate Rho family GTPases by glucosylation, ultimately disrupting the actin cytoskeleton, cell signaling, and leading to cell death. Both TcdA and TcdB are major therapeutic targets for monoclonal antibody-based therapies and are the central diagnostic markers for *C. difficile*-associated disease.

Other names

Clostridioides difficile toxin A (TcdA)Clostridioides difficile toxin B (TcdB)C. difficile toxin A/Blarge clostridial toxins

Direct neutralization of toxin by monoclonal antibody (bezlotoxumab blocks TcdB binding to host cells); Inhibition of toxin-induced cell glucosylation; Preventing toxin-receptor interaction and internalization