Clostridium difficile toxin A. Interactions with mucus and early sequential histopathologic effects in rabbit small intestine.

Clostridium difficile produces two toxins, A (enterotoxic) and B (cytopathic), that are implicated in the pathogenesis of pseudomembranous colitis. However, the relationship of the secretory effect and the early histopathologic events is still unclear. We examined the early histopathologic effect of purified C. difficile toxin A in rabbit ileal loops and correlated the mucosal damage with the secretory response. As early as 2 hours after inoculation, toxin A at 1.0 micrograms caused cytolysis of the basal portion of the apical epithelia cells. Electron microscopy showed the basal portions of the absorptive epithelial cells necrotic. No significant fluid accumulation occurred after 2 or 4 hours in ileal loops inoculated with either 0.1 or 1.0 micrograms toxin A. In contrast, with 3-10 micrograms toxin A there was significant hemorrhagic fluid accumulation after 2 hours that correlated with the severity of the histologic lesions. An early mucoid exudate was demonstrated not to be related to a mucus secretagogue effect of toxin A. Prior exposure of toxin A to rabbit intestinal mucus preparations did not alter its subsequent enterotoxic or cytopathic (Chinese hamster ovary cells) effects. These studies demonstrate that the early intestinal tissue damage by toxin A was dose and time dependent and involved disruption of the basal portions of the absorptive epithelial cells with marked separation of the cells along the mucosal surfaces that preceded the secretory response.