Purpose: The purpose of this study was to evaluate the DuPont™ BAX® System Real-Time PCR Assays for E. coli O157:H7 and Real-Time STEC Suite as rapid detection methods for two pet food formulations (one canine and one feline). Samples used in this study were artificially inoculated with target organisms to ensure matrix inhibition would not cause false results.
Methods: Seven target strains of Escherichia coli(O157:H7, O26, O45, O103, O111, O121, O145) were separately inoculated onto three samples each of pelleted ground pet food at levels determined to return positive results based on previous studies. All samples were stressed for a period of 72 hours at room temperature, then combined with pre-warmed (42°C) System MP Media and incubated for 22 hours at 42°C. Samples were tested both with and without a re-growth step (1:50 dilution of primary enrichment into BHI incubated for 3 hours at 37°C), which was performed to eliminate potential PCR inhibitory compounds. All samples were tested with each of the PCR assays, followed by culture confirmation protocols outlined in the FDA-BAM.
Results: The PCR assays returned positive results for all inoculated samples (canine and feline foods) after the 22-hour primary enrichment, and identical results were returned after re-growth was performed. Therefore, the additional re-growth step is not necessary for this matrix. All positive enrichments were confirmed using the procedures included in the FDA-BAM.
Significance: Overall, the PCR Assay for E. coli O157:H7 and the Real-Time STEC Suite were found to give equivalent results to the reference method using the proprietary enrichment media. Furthermore, the BAX® System method returned results faster than the culture method, significantly decreasing the overall time to result.