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

Clostridioides difficile toxin A (TcdA) and toxin B (TcdB) are the primary virulence factors responsible for the clinical manifestations of C. difficile infection (CDI). These large clostridial toxins function as glucosyltransferases that target and inactivate host Rho-family GTPases, including Rho, Rac, and Cdc42 (Aktories et al., 2017, PubMed: 28846651). This molecular modification leads to the collapse of the actin cytoskeleton, disruption of tight junctions, and induction of apoptosis in intestinal epithelial cells (Di Bella et al., 2016, PubMed: 27653561). The resulting mucosal damage and inflammatory response cause symptoms ranging from mild diarrhea to life-threatening pseudomembranous colitis (StatPearls, 2023, NBK431054). Therapeutic intervention focuses on neutralizing these toxins to prevent cellular damage; for instance, the monoclonal antibody bezlotoxumab binds to TcdB, blocking its interaction with host cell receptors (Wilcox et al., 2017, PubMed: 28121507). Unlike traditional antibiotics, toxin-targeting therapies aim to reduce disease recurrence by protecting the colonic mucosa while the native microbiome recovers (Gerding et al., 2015, PubMed: 25624316). TcdA and TcdB are characterized by a multi-domain structure including a glucosyltransferase domain, a cysteine protease domain, and a receptor-binding domain (UniProt P16154). While TcdA was historically considered the main enterotoxin, clinical evidence suggests TcdB is more essential for human disease pathogenesis (Lyras et al., 2009, PubMed: 19727192). Monitoring for these toxins in stool samples remains the gold standard for diagnosing active infection (CDC, 2023).

Other names

C. difficile toxinsEnterotoxin A and Cytotoxin BLarge clostridial toxinsLCTs

Neutralization of toxins by monoclonal antibodies that bind to the toxin's receptor-binding domains, preventing cellular entry and subsequent inactivation of host Rho GTPases (Wilcox et al., 2017, PubMed: 28121507).