Copyright C 1991, American Society for Microbiology Nontoxigenic Strains of Clostridium difficile Lack the Genes

A total of 39 toxigenic and 20 nontoxigenic strains of Clostridium difficile were tested for the presence of either toxin A or toxin B by the polymerase chain reaction (PCR). Ail toxigenic strains produced cytotoxin as assayed by using highly sensitive fetal lung fibroblasts and were positive for toxin A as well as toxin B in the PCR assay. All nontoxigenic strains failed to produce toxin and were negative in the PCR assay. This study shows that nontoxigenic strains of Clostridium difficile lack the toxin A as well as the toxin B gene. Clostridium difficile, recognized as a major cause of anti-biotic-associated pseudomembranous enterocolitis, pro-duces two toxins. Toxin A, an enterotoxin, causes hemor-rhagic fluid accumulation in rabbit ileal loops and is cytotoxic for cultured fibroblasts. Toxin B is an extremely potent cytotoxin (for a review, see reference 7). Recently it has been showed that the toxin A gene encodes for a 308-kDa protein, in agreement with the molecular mass estimated from polyacrylamide gel electrophoresis (3, 9). The toxin B gene has also been located and sequenced (1, 5)