Clostridium perfringens

The species name, perfringens, is Latin for breaking through, from its association with gas gangrene, where the gas it produces spreads through tissue; the genus name Clostridium refers to the spindle shape of the spore-bearing cell. It is a gram-positive, anaerobic, spore-forming rod, non-motile, and it has the shortest generation time of any known bacterium, dividing about every ten minutes when warm and well fed. Its spores are heat-resistant and survive ordinary cooking.

It was found in 1891 by William Welch at the Johns Hopkins Hospital, during an autopsy, and was first named Bacillus aerogenes capsulatus, then Bacillus welchii, before becoming Clostridium perfringens. It was known first as a cause of gas gangrene; its role in food poisoning was recognised later.

The food-poisoning route is a toxicoinfection, and it depends on the heat-resistant spore. A cooked meat is heated enough to kill the growing cells but not the spores. If the food is then held warm or cooled slowly, the spores germinate and the cells multiply rapidly at their preferred 43 to 47 degrees C, in the middle of the danger zone. When a large number of live cells is eaten, more than about a hundred million, they sporulate in the gut and release Clostridium perfringens enterotoxin, causing cramping pain and diarrhoea eight to twenty-two hours later. The illness is usually mild and resolves within a day, but it is one of the most common causes of food poisoning by volume.

**How it endangers cured meat.** It is not a hazard in a dry-cured product, whose low water activity it cannot tolerate. Its setting is the cooked meat. A cooked ham, a large roast, a cooked sausage or a pot of stock cooled too slowly passes down through its growth range, about 50 to 15 degrees C, and gives surviving spores time to multiply to dangerous numbers. This is why cooked products must be cooled quickly through the danger zone rather than left to cool on their own, and it is one reason nitrite is used in cooked cured meats, since it inhibits this organism as well as botulinum. Like the other handling hazards it belongs to Hygiene Control, a matter of cooling and holding rather than of the cure.

The controls are clear: cool cooked product quickly through the danger zone, to the schedules set for this organism; keep nitrite in cooked cured formulations; and note that freezing and prolonged chilling kill the vegetative cells, so the risk is in the warm, slow middle, not in the cold.