Differential effects of Clostridium difficile toxins on ion secretion and cell integrity in human intestinal cells

Background Toxin A (TcdA), toxin B (TcdB), and binary toxin (CDT) produced by Clostridium difficile (CD) are thought to play a key role in inducing diarrhea. The aim of this study was to investigate the individual and combined roles of CD toxins in inducing enterotoxic and cytotoxic effect. Methods Ion secretion and epithelial damage were evaluated in the Ussing chambers as measure of enterotoxic or cytotoxic effect, respectively, in human-derived intestinal cells. Results When added to the mucosal side of Caco-2 cells, TcdB, but not TcdA, induced ion secretion and its effects increased in the presence of TcdA. CDT also induced ion secretion when added to either the mucosal or serosal compartment. Serosal addition of TcdB induced epithelial damage consistent with its cytotoxic effect. However, mucosal addition of TcdB had similar effects, but only in the presence of TcdA. CDT induced epithelial damage when added to the serosal side of cell monolayers, and this was associated with a late onset but prolonged effect. All data were replicated using human colon biopsies. Conclusions These data indicate that CD, through the combined and direct activity of its three toxins, induces integrated and synergic enterotoxic and cytotoxic effects on the intestinal epithelium.