Clostridium difficile toxin A and Clostridium difficile toxin B (TcdA and TcdB)

Clostridium difficile toxins A and B are large protein exotoxins produced by the Gram-positive anaerobe Clostridium difficile (also known as Clostridioides difficile), responsible for most cases of antibiotic-associated diarrhea and pseudomembranous colitis[1][2][3][7]. These toxins are the main virulence factors, acting through a multi-domain mechanism: they bind to carbohydrate receptors on intestinal epithelial cells, undergo endocytosis, and deliver an N-terminal glucosyltransferase domain into the cytosol[1][5][6]. This domain inactivates Rho family GTPases, leading to disruption of cytoskeletal structure, breakdown of cell–cell junctions, apoptosis, and a strong pro-inflammatory response[1][7]. Toxin B (TcdB) is now recognized as the key pathogenetic agent in human disease, with antibody therapy (bezlotoxumab) approved to reduce recurrence. Both toxins are signature members of the large clostridial toxin family and have become important therapeutic targets due to their central role in C. difficile–associated disease[3][6]. Detection of toxins in stool is used diagnostically; neutralizing antibodies represent the main targeted therapy, but recurring infection and toxin variants continue to present clinical challenges[3][4][6].

Other names

Toxin A (TcdA)Toxin B (TcdB)Large clostridial toxin ALarge clostridial toxin BEnterotoxin A (for TcdA)Cytotoxin B (for TcdB)Clostridioides difficile toxin A and B (alternative taxonomic nomenclature)

Neutralization of toxin activity by monoclonal antibodies (e.g., bezlotoxumab blocks TcdB binding or function); Inhibition of glucosyltransferase activity (investigational small molecules, not yet approved); Inhibition of cellular binding or uptake (antibody or peptide blockade)