Shiga toxin-producing Escherichia coli (STEC) O157:H7 and serogroups O26, O45, O103, O111, O121, and O145 are often referred to as the "top seven" STEC, and these have been declared to be adulterants in beef by the U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS). The aim of this work was to compare the methods described in the USDA FSIS Microbiology Laboratory Guidebook (MLG) to a two-stage Applied Biosystems RapidFinder STEC real-time PCR method to test for the top seven STEC in raw ground beef. The specificity of the RapidFinder workflow that targets non-O157 STEC O-antigen genes, stx, stx, and eae, and E. coli O157-specific targets was determined with 132 top seven STEC strains and 283 exclusion strains. All inclusion strains were positive, and all exclusion strains gave negative results with the RapidFinder assay. Strains carrying all of the known variants of stx and stx, including stx and stx, were also detected. For RapidFinder analysis, 375-g ground beef samples spiked with ≥4 CFU of representative STEC strains were enriched in 1 L of tryptic soy broth (TSB) for 10 h at 42 ± 1°C, and for the MLG method, 325-g samples were similarly spiked and enriched in 975 mL of modified TSB for 15 h at 42 ± 1°C. Following DNA extraction, real-time PCR was performed using RapidFinder Express software, and for the MLG method, the BAX Real-Time PCR STEC Suite and the BAX Real-Time E. coli O157:H7 assay were used with the BAX System Q7 software. Following immunomagnetic separation, presumptive colonies from modified Rainbow agar O157 plates were confirmed by the real-time PCR assays. Results of the RapidFinder and BAX assays were similar; all samples were positive after 10 and 15 h of enrichment, respectively. Isolation and confirmation of isolates was possible on all samples, except that two O111:NM strains could not be isolated from a portion of the inoculated samples. Thus, the RapidFinder system can be used for routine and rapid detection of the top seven STEC in beef.

In recent years, reoccurring Campylobacter-mediated outbreaks of human disease have been linked to undercooked chicken livers. A need exists for interventions to significantly reduce Campylobacter in this widely consumed poultry product. In this study, high pressure processing (HPP) techniques were applied to laboratory-contaminated chicken livers (∼4 × 108 cells per liver) to determine the Campylobacter jejuni–reducing potential of this technology. HPP was able to significantly reduce C. jejuni numbers in chicken livers with the application of 350 MPa for 5 min, resulting in an average reduction of 3.4 log. Unfortunately, when chicken livers were processed in this manner, the surface tissue of the livers turned brown and a fine white foam was produced. A more modest pressure of 250 MPa applied for 10 min resulted in an average reduction in cell numbers of 1.3 log but without an obvious color change in the livers. On average, cold storage conditions (4 and −20°C) were able to produce a 0.2- to 1.3-log reduction, depending on the temperature and storage time. This effect combined with an HPP reduction in an additive fashion. Pulsed HPP techniques failed to produce C. jejuni reductions that exceeded the average reductions compared with constant pressure application using similar time intervals. Hence, HPP is a potential means of reducing C. jejuni numbers in chicken livers, but given its effects on the appearance of the food product at higher pressure levels, it will most likely need to be combined with other intervention techniques. HIGHLIGHTS

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