Problems in the Recovery and Identification of Yersinia from Food

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Abstract
Y. enterocolitica and Y. pseudotuberculosis are emerging foodborne pathogens. Phosphatesaline enrichment of food homogenates at 4°C required about 2 weeks for retrieval of yersinia when present at 10,000/g. Modification by inclusion of 1% sorbitol and 0.15% bile salts increased sensitivity 10-fold and extended the recovery period. MacConkey was superior to bismuth-sulfite, Salmonella-Shigella, Hektoen, and Levine EMB agars for isolation. Incubation at 26°C was more satisfactory for recovery and characterization than 37°C. Isolates were first screened in TSI, mannitol, and lysine which eliminated 75% of interfering cultures. Of 25 biochemicals evaluated, urea, arginine, motility (at 26 and 37C°), and phenylalanine were most useful for confirmation. Cultures isolated from foods were classified into 2 groups (1) giving negative reactions in citrate, raffinose, melibiose, and gelatin; and (2) giving positive reactions in the above biochemicals. The former resembled classical European strains of Y. enterocolitica. The latter were more frequently recovered and designated Y. enterocolitica-like bacteria.