USE OF UNIVERSAL PREENRICHMENT MEDIUM SUPPLEMENTED WITH OXYRASETM FOR THE SIMULTANEOUS RECOVERY OF ESCHERICHIA COLI O157:H7 AND YERSINIA ENTEROCOLITICA

Abstract

Universal Preenrichment (UP) medium was used successfully for the simultaneous recovery of two strains each of Escherichia coli O157:H7 and Yersinia enterocolitica in the presence of Listeria monocytogenes and Salmonella typhimurium. E. coli O157:H7 and Y. enterocolitica populations reached ca. 108 CFU/ml in UP medium in 18 h from an initial level ofca. 102 CFU/ml. Addition of OxyraseTM enhanced the growth of both E. coli O157:H7 strains and one strain of Y. enterocolitica. These three strains were able to recover from heat injury by 6 h when 24‐h cultures were tested, but not when 18‐h cultures were used. Injured and noninjured E. coli O157:H7 could be recovered from artificially inoculated food samples (shredded cheddar cheese, turkey ham, hot dogs, mayonnaise, and ground beef) in UP medium supplemented with OxyraseTM (UPO) by 18 h using immunoblotting. Y. enterocolitica could be recovered from turkey ham, hog dogs, and mayonnaise by direct plating on CIN agar from UPO medium. However, recovery of Y. enterocolitica from shredded cheddar cheese and ground beef required subsequent selective enrichment in sorbitol bile broth and isolation on Cefsulodin Irgasan Novobiocin agar (CIN). UPO medium can be used for simultaneous detection of E. coli O157:H7 and Y. enterocolitica from foods. However, subsequent selective enrichment and isolation on selective plating media are required for isolation of Y. enterocolitca from raw foods containing high population levels of background microflora.