Effects of Clostridium difficile toxins A and B in rabbit small and large intestine in vivo and on cultured cells in vitro.

Clostridium difficile is recognized as the major cause of antibiotic-associated colitis. C. difficile produces two toxins, A (enterotoxin) and B (cytotoxin), that are implicated in the pathogenesis of the colitis. We examined the dose responses, time course, and synergism of these two toxins in ligated rabbit intestinal loops and in tissue culture. In rabbit small intestinal loops, toxin A caused histologically demonstrable intestinal tissue damage as early as 2 h. The secretory response greater than or equal to 8 h was similar to that of a cholera toxin control. The effect of toxin A on tissue damage or secretion was seen even if toxin was removed after 5 min. Purified toxin A caused significant net accumulation of sodium, chloride, potassium, and total protein and slightly increased osmolality of the fluid content at 6 h; these effects were similar to those caused by crude C. difficile culture filtrates containing toxins A and B. Crude C. difficile toxin caused fluid accumulation with a delayed time course in the rabbit large intestine, and in contrast to its effect in small intestine, crude toxin caused net accumulation of bicarbonate and increased pH. In tissue culture, toxin A caused a rounding up of CHO and T-84 colonic carcinoma cells. A monoclonal antibody (PCG-4) that has no effect on tissue culture cytotoxicity with toxins A and B completely inhibited the secretory and tissue-damaging effects in the intestine. Toxins A and B were synergistic in the gut only at high doses of toxin B (greater than or equal to 10 micrograms/ml), and they were additive in tissue culture. The cytopathic effect in tissue culture was not consistently associated with trypan blue uptake. The cytopathic effect of toxin A in tissue culture did not appear to involve inhibitable Ca2+-dependent or prostaglandin synthesis pathways or intact microfilament or microtubule function for its activity and was not inhibited by reducing or lysosomotropic agents. Our results suggest that toxins A and B have independent and distinct effects in vivo and in vitro.