The effectiveness of current antimicrobial interventions used in reducing the prevalence or load of Escherichia coli O157 and indicator organisms on cattle hides and carcasses at two commercial bee...

Escherichia coliO157:H7 is a Shiga toxin (stx)-producingE. coli(STEC) strain that has been classified as an adulterant in U.S. beef. However, numerous other non-O157 STEC strains are associated with diseases of various severities and have become an increasing concern to the beef industry, regulatory officials, and the public. This study reports on the prevalence and characterization of non-O157 STEC in commercial ground beef samples (n= 4,133) obtained from numerous manufacturers across the United States over a period of 24 months. All samples were screened by DNA amplification for the presence of Shiga toxin genes, which were present in 1,006 (24.3%) of the samples. Then, culture isolation of an STEC isolate from all samples that containedstx₁and/orstx₂was attempted. Of the 1,006 positive ground beef samples screened forstx, 300 (7.3% of the total of 4,133) were confirmed to have at least one strain of STEC present by culture isolation. In total, 338 unique STEC isolates were recovered from the 300 samples that yielded an STEC isolate. 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), and the presence of the large 60-MDa virulence plasmid (espP,etpD,toxB,katP,toxB). The isolates were also characterized by use of a pathogenicity molecular risk assessment (MRA; based on the presence of various O-islandnlegenes). Results of this characterization identified 10 STEC isolates (0.24% of the 4,133 total) that may be considered a significant food safety threat, defined by the presence ofeae,subA, andnlegenes.

The hide and carcass hygiene of cull cattle at slaughter in four geographically distant regions of the United States was examined from July 2005 to April 2006 by measuring the aerobic plate counts (APC) and the prevalences and loads of Salmonella and Escherichia coli O157:H7. The geometric mean log ₁₀ APC CFU/100 cm ² levels on hides and preevisceration and postintervention carcasses ranged from 6.17 to 8.19, 4.24 to 6.47, and 1.46 to 1.96, respectively, and were highest in the summer ( P < 0.0001). The average prevalences of Salmonella on hides and preevisceration and postintervention carcasses were 89.6% (95% confidence interval [CI], 85.1 to 94.0), 50.2% (95% CI, 40.9 to 59.5), and 0.8% (95% CI, 0.18 to 1.42), respectively. The prevalences of E. coli O157:H7 were 46.9% (95% CI, 37.3 to 56.6) and 16.7% (95% CI, 9.8 to 23.6) on hides and preevisceration carcasses, respectively. Examination of the concomitant incidence of Salmonella and E. coli O157:H7 showed that, on average, 33.3% (95% CI, 15.9 to 69.8) of cattle hide and 4.1% (95% CI, 0.98 to 17.3) of preevisceration carcass samples were contaminated with both pathogens. The pathogen prevalence on hides and carcasses was not significantly affected by the season; however, significant differences were observed between plants with respect to the incoming pathogen load and the ability to mitigate hide-to-carcass transfer. In spite of these differences, postintervention carcass contamination was significantly reduced ( P < 0.001), likely as a result of the use of one or more of the processing interventions employed at each of the four processing plants examined.

Hide has been established as the main source of carcass contamination during cattle processing; therefore, it is crucial to minimize the amount of Escherichia coli O157:H7 on cattle hides before sl...