Yersinia spp. and numbers, with particular reference to Y. enterocolitica bio/serotypes, occurring on Irish meat and meat products, and the influence of alkali treatment on their isolation.

Samples (n = 340) of Irish meat and meat products were examined to determine the incidence and initial numbers of Yersinia spp. present. In cases where no typical Yersinia colonies were observed, samples were cold enriched up to 21 days at 4 degrees C and streaked out on CIN agar with and without post-enrichment alkali treatment. The highest isolation rates of Yersinia were found using post-enrichment alkali treatment and an incubation temperature of 37 degrees C. All Yersinia isolates were identified to species level and Y. enterocolitica isolates were biotyped and serotyped. Pathogenic isolates (biotypes 1B-5) were examined for the presence of a virulence plasmid using dye binding reactions and agglutination tests. The incidence of Yersinia spp. was high on raw (89%) and cooked meats (49%) obtained fromdelicatessen counters but lower in pre-packaged cooked meats (18.8%). Initial numbers of Yersinia were generally < 2.7 log10cfu/g on raw meats and < 0.7 log10cfu/g on cooked.