Yersinia enterocolitica

The genus is named after Alexandre Yersin, who identified the plague bacillus in 1894; the species name, enterocolitica, refers to the gut inflammation it causes. It is a gram-negative rod of the family Enterobacteriaceae, a facultative anaerobe, and, like Listeria, it is psychrotrophic: it grows at refrigeration temperature and below, and it is motile at cool temperatures but not at body heat. It was first described in 1934, by McIver and Pike.

Its relevance to the curesmith is its reservoir. Pigs are its principal host, and it lives in their tonsils, tongue, intestines and lymph nodes, from which it contaminates the carcass at slaughter, particularly during the handling of the head and pluck. The pathogenic type known as 4/O:3 is the one that most often affects people. Eating raw or undercooked pork is the usual route to yersiniosis, a gastroenteritis that most affects young children, sometimes with a form resembling appendicitis in older children, and occasionally followed by reactive arthritis. In Europe it ranks third among bacterial causes of enteric illness, after Salmonella and Campylobacter.

**How it endangers cured meat.** It is both a pork hazard and a cold hazard. Because pigs carry it and it grows in the cold, raw and chilled pork are its vehicle, and it can multiply on stored raw pork at refrigeration temperature, even alongside the lactic acid bacteria that would slow most competitors. For the curesmith it is a hazard of the raw material and the cold chain rather than a survivor of a finished product: thorough cooking kills it, and the drying and acidification of a proper cure remove it. The risk is in chilled raw pork and in cross-contamination from it, which places it under Hygiene Control.

The defences follow from that: clean slaughter and dressing that keep the head, tongue and tonsils away from the meat; a reliable cold chain; cooking where the product is cooked; and separation of raw pork and its juices from finished product.