Improved procedure for recovery of Yersinia enterocolitica from meats

Abstract

A 1- to 3-day enrichment-KOH postenrichment procedure was evaluated and found to be as effective in recovering Y. enterocolitica from meats as a 14- to 21-day cold enrichment procedure, with or without KOH postenrichment. The shortened procedure consists of enriching 1.0- and 25-g samples of meat in phosphate-buffered saline (pH 7.2) at 25°C. After incubation (48 and 72 h for 1.0-g samples and 24 and 48 h for 25-g samples), 0.5-ml portions of enrichment culture were treated with 4.5 ml of 0.25% KOH-0.5% NaCl for 2 min and 0.5% KOH-0.5% NaCl for 15 s, and 0.1-ml portions of treated culture were plated onto MacConkey or CIN agars or both. The procedure effectively recovered 2 to 12 cells of a number of both mouse-virulent and avirulent strains per g of ground beef with aerobic plate counts of approximately 106 to 107 CFU/g. Similarly, the procedure isolated both likely virulent and avirulent strains from porcine tongues (aerobic plate counts of 105 to 107 CFU/g) naturally contaminated with Y. enterocolitica. The organism was isolated from the tongues at similar rates by both shortened enrichment and cold enrichment procedures. Eight tongues were positive for serotype O:5,27 strains that agglutinate with WA-specific absorbed antiserum, an antiserum specific for mouse-virulent Y. enterocolitica, indicating that the oral cavity of swine is a reservoir of likely virulent serotype O:5,27 strains.