Yersiniosis Associated with Tofu Consumption: Serological, Biochemical and Pathogenicity Studies of Yersinia enterocolitica Isolates

Abstract

Between December 1981 and February 1982 in the Seattle area, 87 individuals ranging in age from 2 months to 74 years developed clinical symptoms of yersiniosis (abdominal cramps, fever, headache, diarrhoea and photosensitivity). The outbreak was related to consumption of tofu (soybean curd). The epidemiologial evidence and investigational details are not included in this paper which is concerned with the results of detailed analysis on 6 of the strains isolated from patients during the outbreak. Of these 6 strains, 4 were serotype O:8 and 2 were O:Tacoma. It appears these were the only isolates from patients and it was concluded that the two serotypes were "involved" in the outbreak. All the strains were similar in biotype but 3 harboured a 42 × 106 plasmid; two of these autoagglutinated at 37 °C, were lethal in the appropriate infant and adult mouse tests and were Sereny-test positive. The other strains were negative in these tests but 2 others (i.e. 4 in all) shared with these the property of producing heat-stable enterotoxin and all 6 invaded HeLa cells.Of 112 strains recovered at the manufacturing site of the tofu, 2 serotype O:8 strains were found which were indistinguishable from the clinical isolates, carried the 42 × 106 plasmid and were positive in the virulence tests listed above. These were isolated from water used in processing the food and were thought epidemiologically significant. The likely source of the O:Tacoma strain was not traced. The importance of virulent plasmids and lipase production in virulence tests is discussed.P.C.B. Turnbull