CLOSTRIDIUM-DIFFICILE TOXIN-B IS MORE POTENT THAN TOXIN-A IN DAMAGINGHUMAN COLONIC EPITHELIUM IN-VITRO

Toxin A but not toxin B, appears to mediate intestinal damage in anima l models of Clostridium difficile enteritis, The purpose of this study was to investigate the electrophysiologic and morphologic effects of purified C. difficile toxins A and B on human colonic mucosa in Ussing chambers, Luminal exposure of tissues to 16-65 nM of toxin A and 0.2- 29 nM of toxin B for 5 h caused dose-dependent epithelial damage, Pote ntial difference, short-circuit current and resistance decreased by 76 , 58, and 46%, respectively, with 32 nM of toxin A and by 76, 55, and 47%, respectively, with 3 nM of toxin B, when compared with baseline ( P < 0.05), 3 nM of toxin A did not cause electrophysiologic changes. P ermeability to [H-3]mannitol increased 16-fold after exposure to 32 nM of toxin A and to 3 nM of toxin B when compared with controls (P < 0. 05). Light and scanning electron microscopy after exposure to either t oxin revealed patchy damage and exfoliation of superficial epithelial cells, while crypt epithelium remained intact. Fluorescent microscopy of phalloidin-stained sections showed that both toxins caused disrupti on and condensation of cellular F-actin, Our results demonstrate that the human colon is similar to 10 times more sensitive to the damaging effects of toxin B than toxin A, suggesting that toxin B may be more i mportant than toxin A in the pathogenesis of C. difficile colitis in m an.