Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2014
Publication Date: 6/18/2014
Citation: Wasilenko, J.L., Fratamico, P.M., Sommers, C.H., Demarco, D., Varkey, S., Rhoden, K., Tice, G. 2014. 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. Frontiers in Cellular and Infection Microbiology. DOI: 10.3389/fcimb.2014.00081. Interpretive Summary: Bacteria known as Shiga toxin-producing Escherichia coli (STEC) and Salmonella are food-borne pathogens commonly associated with beef, and they have been associated with numerous outbreaks and cases of illness associated with food of bovine origin. Thus, rapid and reliable methods are needed to determine their prevalence in beef and to ensure food safety. In this study commercially available polymerase chain reaction (PCR)-based methods were used to conduct a survey to determine the presence of these important food-borne pathogens in retail ground beef. Genes associated with STEC were identified in over portion of the samples and the bacteria were isolated from 4 out of 308 ground beef samples. Over 9% (28/308) of the ground beef samples contained Salmonella. Results of this investigation demonstrated that the PCR-based methods for detection of STEC and Salmonella are rapid and accurate and can be used for screening for these pathogens in beef and potentially other foods, as well. This study also provides information on the prevalence of these pathogens, which will be useful in risk assessments for STEC and Salmonella in beef.
Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) and Salmonella are food-borne pathogens commonly associated with beef, and reliable methods 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 real-time PCR assays: BAX® System real-time STEC suite, BAX System real-time PCR assay for E. coli O157:H7 and O157:H7 MP assay and 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 were PCR positive for Salmonella were inoculated into RV broth, incubated for 18 h at 42'C, and then plated onto XLT-4 agar. Presumptive positive STEC and Salmonella colonies were confirmed using the BAX assays. Results of the BAX STEC assays showed 20/308 (6.5%) 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. Three (1.0%) of the samples were positive using the E. coli O157:H7 real-time assay, and 28 (9.1%) were positive for Salmonella. From the PCR positive samples, STEC O103 and E. coli O157:H7 were isolated from 2/6 and 2/3 samples, respectively. Salmonella isolates were recovered and confirmed from 27 of the 28 Salmonella PCR positive samples, the isolates were serotyped, and the antibiotic resistance profiles were determined. Results demonstrate that the BAX PCR-based real-time PCR assays for non-O157 STEC and O157:H7 are rapid and sensitive methods for screening for these pathogens in beef and potentially other foods, as well.