Investigation of Yersinia enterocolitica, Yersinia enterocolitica-like bacteria, and thermotolerant campylobacters in Norwegian pork products

Abstract

Altogether, Yersinia spp. were isolated from 41 (27.0%) of 152 samples of retail pork products. Thermotolerant campylobacters were not detected in this study. Yersinia spp. were recovered from 39 (30.7%) of the 127 raw pork samples and from two (8.0%) of the 25 cooked pork samples investigated. Sixty distinct strains were isolated. Y. enterocolitica comprised 58.3% of the total number, followed by Y. intermedia (20.0%), Y. kristensenii (18.3%), and Y. frederiksenii (3.3%). The serotyping scheme employed enabled us to type 91.7% of the strains. The most frequently isolated serotype was O:5 which comprised 20.0% of the total number, followed by O:7, 8 (11.7%), and O:11 (8.3%). Only one strain of O:3/biotype 4, the predominant human pathogen in Europe, was isolated. This was the only isolate which provoked positive reaction in the autoagglutination virulence assay. A second O:3 strain was classified as Y. kristensenii. Optimal recovery of Yersinia spp. was achieved using three-weeks cold enrichment in addition to a two-step procedure based on pre-enrichment in a low-selectivity medium (8 days, 4°C) followed by selective enrichment in modified Rappaport broth (4 days, 20–25°C). The results indicate that Yersinia spp. are more likely to be isolated from foods with a high level of coliforms than from foods with low coliform counts.