Yersinia enterocolitica and Yersinia enterocolitica-like bacteria in Norwegian slaughter pigs

Yersinia spp. were isolated from the tonsils of 200 (43.4%) of 461 freshly slaughtered pigs. Y. enterocolitica comprised 92.7% of the total number of isolates, while Y. kristensenii, Y. intermedia, and Y. pseudotuberculosis comprised 6.3%, 0.5% and 0.5% respectively. Fifteen different serotypes were recognized. Serotype O:3 comprised 70.9% of the total number, followed by O:5 (6.8%), and O:6,30 (6.3%). Y. enterocolitica O:3/biotype 4, the predominating human pathogen in Europe, was isolated from 31.7% of the pigs examined. 67 (45.9%) of these isolates were potentially virulent as judged by the autoagglutination virulence assay. Three-week cold enrichment in a low-selectivity medium was the most efficient single method for recovery of Y. enterocolitica serotype O:3/biotype 4, Y. enterocolitica biotype 1, and Y. kristensenii. However, optimal recovery was achieved using a multi-method isolation technique, including a two-step procedure based on pre-enrichment followed by selective enrichment in a modified Rappaport broth.