Background Food poisoning caused by C. perfrin-gens is also toxin mediated. It differs, however, from those described previously in that toxin is formed in the intestine after ingestion of the bacteria. Like other clostridia, it is anaerobic, gram positive, and spore forming. There are five types, classified A-E
according to the enterotoxin formed; type A is the one that causes FP. Some strains, but not generally those that cause FP, can cause gas gangrene. Clos-tridium perfringens is primarily found in soil and is transmitted to animals and man by ingestion of vegetables and other plants. It is thus commonly found in the intestine of man and animals. When animals are eviscerated, the organism contaminates the inside of the carcass. Flies can transmit the organism to food.
Clostridium perfringens FP is common. Fortunately, it is rarely fatal except in those who are debilitated or immunocompromised.
Growth and survival Clostridium perfringens does not tend to multiply on the surface of raw meat. It grows optimally at warm temperatures of approximately 43-47 °C (range, 20-50 °C) and low oxygen levels found in the interior of a cooked dish. The cooking process will have driven off oxygen and thus facilitated sporulation and subsequent growth of the organism. Vegetative cells are not resistant to heat, but spores of the FP strains of C. perfringens can survive boiling for several hours. If cooling is slow, vegetative cells reform and grow rapidly. After ingestion, toxin is formed from multiplying cells in the intestine, although both toxin and vegetative cells appear to be necessary to produce symptoms.
Clinical features and characteristic sequence of events A casserole is prepared containing, among other ingredients, cubed meat. It is heated to boiling and allowed to cook for 1 or 2 h until ready. However, it is not needed immediately, and because of its bulk and lack of refrigeration facilities it is left overnight in a warm kitchen. It is warmed the next day before serving. Symptoms of diarrhea with abdominal pain begin 8-24 h later. The illness may last only a few hours, and there are no sequelae, except in those who are already debilitated.
Diagnosis The organism can be cultured from the stools of affected people and should be compared with that isolated from food for toxin production. Enterotoxin detection in stools is important confirmatory evidence. The organism has to be detected in high numbers in food to be significant. Molecular typing methods are available to compare isolates from food and feces.
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