(462) This bacterium of which two species occur in the pig, Y. pseudotuberculosis and Y. enterocolitica, is found in the intestine. It may cause food poisoning in the human. Infection takes place by mouth and the organism is passed in the faeces for 1 to 10 weeks. It may reside in the tonsils for long periods. It normally causes little or no disease but it has been associated, with outbreaks of diarrhoea in weaned pigs. Y. enterocolitica causes inflammation of the small and large intestines and Y. pseudotuberculosis causes small tiny abscesses throughout the carcase. The main significance of the organism relates to cross reactions that occur in agglutination tests for brucellosis. Pigs that are carrying the organism are likely to react positively. If this is the case it is necessary to determine the point in the rearing system when exposure takes place and break the cycle by management control. There is a response to antibiotics including tetracyclines, synthetic penicillins and fluoroquinolones.