Purpose: The objective of this study was to compare the PCR-Rainbow agar (PCR-RB) method to a PCR-immunoblot (PCR-IB) method for the detection and isolation of STEC from meat samples.
Methods: Retail meat samples, including raw meat (ground beef, pork sausages, pork kabobs) and ready-to-eat (RTE) meat (salami, pepperoni, summer sausages) were acquired and inoculated with STEC strains of O26, O45, O103, O11, O121, O145, and O157, at low (1 to 5 CFU/25g) and high levels (10 to 50 CFU/25g). Samples were enriched in modified tryptone soya broth (supplemented with vancomycin and cefsulodin after 4 h enrichment time) for a total of 20 to 24 h at 42±0.5°C and assayed via PCR-RB and PCR-IB. All inoculated samples were subjected to culture isolation regardless of the PCR result.
Results: For RTE meat samples (n=48), both PCR-RB and PCR-IB were equally effective in screening and isolating STEC. In total, 12 of 20 low and 23 of 23 high inoculated samples were positive, achieving 100% sensitivity, 100% efficacy, and 0% false negative rate. For raw meat samples (n=48), the PCR screening had 100% agreement between the two methods in identifying 15 of 20 low and 23 of 23 high inoculated samples. The immunoblot isolation procedure, however, was more effective in isolating STEC from raw meat (100% sensitivity, 100% efficacy, and 0% false negative rate) compared to the PCR-RB isolation procedure (78.9% sensitivity, 83.3% efficacy, and 21.2% false negative rate).
Significance: The results of this study demonstrated that the immunoblot isolation procedure can be considered an effective alternative to standard direct plating methods for isolating STEC from potentially contaminated meat samples.