Incidence of Yersinia enterocolitica in raw milk in eastern France.

A total of 75 raw milk samples collected from a central dairy or from retailers in Alsace, France, were analyzed for the presence of Yersinia enterocolitica. Three procedures were used: enrichment at 4 degrees C for 1 month; enrichment in modified Rappaport medium at room temperature for 72 h after a preenrichment at 4 degrees C for 1 month; and enrichment in a new medium containing sucrose, tris(hydroxymethyl)aminomethane, sodium azide, and ampicillin (PSTA) at 28 degrees C for 48 h after a preenrichment at 4 degrees C for 1 month. Isolation of Y. enterocolitica was made on Hektoen medium plus ampicillin. Sixty-one samples were positive (81.4%), but the PSTA medium produced the greatest number of isolates. Biochemical, serological, and phage typing of 40 isolates showed that chemotype 1 and serogroup O:5 were predominant. In seven cases, two different strains were obtained from the same samples. Most of the 66 isolates tested for their antimicrobial susceptibility were resistant to ampicillin and carbenicillin, and all were sensitive to tetracycline, chloramphenicol, streptomycin, sulfonamides, and mercuric ions.