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United States Department of Agriculture

Agricultural Research Service


Location: Molecular Characterization of Foodborne Pathogens

Title: Detection of Shiga toxin-producing Escherichia coli (STEC) O157:H7, STEC serogroups O26, O45, O103, O111, O121, and O145, and Salmonella in naturally-contaminated ground beef using the BAX system-based PCR kits

item Wasilenko, Jamie
item Fratamico, Pina
item Sommers, Christopher
item Demarco, Daniel -
item Varkey, Stephen -
item Rhoden, Kyle -
item Tice, George -

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 20, 2013
Publication Date: N/A

Technical Abstract: Shiga toxin-producing E. coli (STEC) and Salmonella are important food-borne pathogens commonly associated with beef. Rapid and sensitive methods for detection of these pathogens are needed to determine their prevalence in beef and to ensure food safety. Retail ground beef was tested for the presence of E. coli O157:H7, STEC serogroups O26, O45, O103, O111, O121, and O145, and Salmonella using BAX system-based PCR assays. Ground beef (325 g) samples were enriched in 1.5 L of TSB with 2 mg/L novobiocin at 42°C for 18 h, and then screened using the BAX System Real-Time PCR Assays – STEC Suite, the BAX System real-time PCR assay for E. coli O157:H7 and O157:H7 MP assay, and the BAX System PCR assay for Salmonella 2. Samples positive for STEC target genes by the BAX assays were subjected to immunomagnetic separation (IMS) and plating onto modified Rainbow Agar O157. Enrichments that tested positive for Salmonella using the BAX Salmonella assay were inoculated into RV broth, incubated for 18 h at 42'C, and the cultures were plated onto XLT-4 agar plates. Presumptive positive STEC and Salmonella colonies were confirmed using the BAX assays. Results of the BAX STEC assays showed 19/308 (6.2%) of samples positive for both the Shiga toxin (stx) and intimin (eae) genes; 4 (1.3%) for stx, eae, and O26; 1 (0.3%) for stx, eae, and O45; 3 (1%) for stx, eae, and O103; and 1 (0.3%) for stx, eae, and O145. There were also 3 samples positive for stx, eae, and more than one STEC serogroup. Two (0.6%) of the samples were positive for E. coli O157:H7, and 28 (9.1%) were positive for Salmonella. From the BAX PCR assay positive samples, STEC O103 and E. coli O157:H7 were isolated from 2/3 and 2/2 samples, respectively. Salmonella isolates were recovered and confirmed from 27 of the 28 Salmonella BAX positive samples, and the isolates were serotyped. Results of this work demonstrate that the BAX PCR-based assays for non-O157 STEC, O157:H7, and Salmonella are rapid and sensitive methods for screening for these pathogens in beef and potentially other foods, as well. A total of 4.5% of samples were positive for either O157:H7 or one or more of the top six non-O157 STEC. There were 9.1% of samples positive for Salmonella, and Salmonella strains were more easily isolated from the enrichments compared to the non-O157 STEC, albeit IMS was used on non-O157 PCR positive samples.

Last Modified: 4/18/2014
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