Purpose: The purpose of this AOAC OMA Collaborative Study was to compare the assay to the USDA/FSIS-MLG for raw ground beef in 25-g and 375-g test portions.
Methods: This new method was evaluated in a multilaboratory collaborative study with 15 participating laboratories representing government, academia and industry. Each test portion size evaluated was artificially contaminated with Salmonella at 3 inoculation levels: a low-level inoculum of 0.2-2 CFU/test portion, a high-level inoculum 2-5 CFU/test portion and an un-inoculated control level 0 CFU/test portion. Assay samples were confirmed following the traditional confirmation procedures and an alternative confirmation procedure, by directing streaking the primary enrichments onto IBISA and ASAP chromogenic agar.
Results: In this study, 828 samples were analyzed by both the assay and the USDA/FSIS-MLG method for a total of 1,656 test portions tested. Of the 1,656 unpaired replicates, 475 were presumptive positive by the assay method, with 475 confirmed positive samples. Comparatively, there were 411 confirmed positive replicates by the USDA/FSIS-MLG reference method. Statistical analysis was conducted according to the Probability of Detection (POD) and the Relative Limit of Detection (RLOD) and no statistically significant difference was observed between the new and reference methods. There was no difference in the recovery of Salmonella on the chromogenic agars compared to the reference agars.
Significance: For both test portion sizes evaluated, the new method produced results comparable to the reference methods for the rapid detection of Salmonella in a variety of foods and environmental samples.