Comparative experiments to examine the effects of heating on vegetative cells and spores of Clostridium perfringens isolates carrying plasmid genes versus chromosomal enterotoxin genes

Clostridium perfringens enterotoxin (CPE) is an important virulence factor for both C. perfringens type A food poisoning and several non-food-borne hu man gastrointestinal diseases. Recent studies have indicated that C. perfri ngens isolates associated with food poisoning carry a chromosomal cpe gene, while non-food-borne human gastrointestinal disease isolates carry a plasm id cpe gene. However, no explanation has been provided far the strong assoc iations between certain cpe genotypes and particular CPE-associated disease s. Since C. perfringens food poisoning usually involves cooked meat product s, we hypothesized that chromosomal cpe isolates are so strongly associated with food poisoning because (i) they are more heat resistant than plasmid cpe isolates, (ii) heating induces loss of the cpe plasmid, or (iii) heatin g induces migration of the plasmid cpe gene to the chromosome, When me test ed these hypotheses, vegetative cells of chromosomal cpe isolates were foun d to exhibit, on average approximately twofold-higher decimal reduction val ues (D values) at 55 degrees C than vegetative cells of plasmid cpe isolate s exhibited. Furthermore, the spores of chromosomal cpe isolates had, on av erage, approximately 60-fold-higher D values at 100 degrees C than the spor es of plasmid cpe isolates had. Southern hybridization and CPE Western blot analyses demonstrated that all survivors of heating retained their cpe gen e in its original plasmid or chromosomal location and could still express C PE, These results suggest that chromosomal cpe isolates are strongly associ ated with food poisoning, at least in part, because their cells and spores possess a high degree of heat resistance, which should enhance their surviv al in incompletely cooked or inadequately warmed foods.