Purpose: The objective of this study was to evaluate the performances of a newly developed PCR based method for the simultaneous detection of STEC Top 6, E. coli O157:H7 and Salmonella in 375-g test portions of raw beef products from a single enrichment, in comparison to the USDA FSIS reference methods.
Methods: The evaluation consisted of method comparison between the alternate method and the USDA/FSIS reference methods for 2 different food matrices (ground beef-GB- and beef trim-BT). The alternate method was conducted at 2 different incubation times, 10 h and 20 h, one temperature 41.5°C, and presumptive positive results for Salmonella were confirmed by 3 different strategies.
Results: Low levels of contamination were between 0.60 & 0.72 CFU/test portion for Salmonella, and 0.43 and 0.49 CFU/test portion for STEC (E. coli O157:H7 and O45) in GB and BT, respectively. For each of the incubation times and for both levels of contamination, low and high (10x low), the PCR based method detected all the contaminated samples for both Salmonella and STEC. All the uncontaminated samples were showed negative by both methods. The statistical analysis with POD (Probability of Detection) showed the PCR-based method to be as good as the USDA reference methods for all the bacterial targets and at both incubation times. All the confirmation methods used for Salmonella isolation were showed equivalent in the confirmation of the PCR screening results.
Significance: This new molecular method was fast and accurate for the simultaneous detection of STEC Top 7 and Salmonella in beef samples.