Prevalence and Characterization of Non-O157 Shiga Toxin Producing Escherichia coli Isolated from Commercial Ground Beef in the United States – Joseph M. Bosilevac and Mohammad Koohmaraie in Appl. Environ. Microbiol. doi:10.1128/AEM.02833-10

Abstract – Escherichia coli O157:H7 is a Shiga toxin (stx) producing E. coli (STEC) that has been classified as an adulterant in U.S. beef. However, numerous other non-O157 STEC are associated with diseases of varying severity, and have become an increasing concern to the beef industry, regulatory officials and the public. This study reports the prevalence and characterization of non-O157 STEC in commercial ground beef (n=4,133) obtained from numerous manufacturers across the U.S. for a period of 24 months. All samples were screened by DNA amplification for the presence of Shiga toxin genes, which were present in 1006 (24.3%) of the samples. Then culture isolation of a STEC from all samples that contained stx1 and/or stx2 was attempted. Of the 1006 stx screened positive ground beef samples, 300 (7.3% of the total 4,133) were confirmed to have at least one strain of STEC present by culture isolation. In total 338 unique STEC isolates were recovered in the 300 samples that yielded a STEC. All unique STEC isolates were serotyped, and were characterized for the presence of known virulence factors. These included Shiga toxin subtypes, intimin subtypes, and accessory virulence factors related to adherence (saa, iha, lifA), toxicity (cnf, subA, astA), iron acquisition (chuA), the presence of the large 60MDa virulence plasmid (espP, etpD, toxB, katP, toxB) and a pathogenicity molecular risk assessment (MRA, based on presence of various O-Island nle genes). Results of this characterization identified ten STEC (0.24% of total 4,133) that may be considered a significant food safety threat defined by the presence of eae, subA, and nle genes.