Enrichment Procedures and Plating Media for Isolation of Yersinia enterocolitica†

Abstract

A shortened enrichment procedure (25°C for 24 h) was compared with cold enrichment procedures (4°C for 1 to 3 weeks) and direct plating for isolation of Yersinia enterocolitica from commercial ground meat samples. The combined data of all recovery procedures showed that this organism was isolated from 34% of the ground beef samples. The highest isolation rate was 32% for the 4°C/3-week enrichment, followed by 28% for the 4°C/2-week enrichment, 26% for the 25°C/24-h enrichment, 22% for the 4°C/1-week enrichment, and 10% for direct plating. No significant differences (P > 0.05) in isolation rate occurred between the 4°C/3-week, 4°C/2-week, 25°C/24-h, and 4°C/1-week enrichments. The combined data of all recovery procedures showed that Y. enterocolitica was isolated from 64% of ground pork samples. The highest isolation rate was 48% for the 4°C/3-week enrichment, followed by 40% for the 25°C/24-h enrichment, 34% for the 4°C/2-week enrichment, 24% for the 4°C/1-week enrichment, and 24% for direct plating. No significant differences (P > 0.05) in isolation rate occurred between the 4°C/3-week, 25°C/24-h, and 4°C/2-week enrichments. During the plating phase of the experiment, the efficiency of a dye-containing, Yersinia-selective medium (KV202) was compared with that of a commercially available cefsulodin-irgasan-novobiocin medium. Recovery rates were similar for both media. However, KV202 agar differentiated Y. enterocolitica from such contaminating bacteria as Enterobacter, Serratia, and Salmonella by colony morphologic characteristics and color.