Clostridium perfringens enterotoxin is the major virulence factor involved in the pathogenesis of C. perfringens type A food poisoning and several non-food-borne human gastrointestinal illnesses. The enterotoxin gene, cpe, is located on the chromosome of food-poisoning isolates but is found on a large plasmid in non-food-borne gastrointestinal disease isolates and in veterinary isolates. To evaluate whether the cpe plasmid encodes its own conjugative transfer, a C. perfringens strain carrying pMRS4969, a plasmid in which a 0.4-kb segment internal to the cpe gene had been replaced by the chloramphenicol resistance gene catP, was used as a donor in matings with several cpe-negative C. perfringens isolates. Chloramphenicol resistance was transferred at frequencies ranging from 2.0 x 10(-2) to 4.6 x 10(-4) transconjugants per donor cell. The transconjugants were characterized by PCR, pulsed-field gel electrophoresis, and Southern hybridization analyses. The results demonstrated that the entire pMRS4969 plasmid had been transferred to the recipient strain. Plasmid transfer required cell-to-cell contact and was DNase resistant, indicating that transfer occurred by a conjugation mechanism. In addition, several fragments of the prototype C. perfringens tetracycline resistance plasmid, pCW3, hybridized with pMRS4969, suggesting that pCW3 shares some similarity to pMRS4969. The clinical significance of these findings is that if conjugative transfer of the cpe plasmid occurred in vivo, it would have the potential to convert cpe-negative C. perfringens strains in normal intestinal flora into strains capable of causing gastrointestinal disease.