Purpose: The purpose of this internal validation was to evaluate the robustness, product consistency, stability, instrument variation and inclusivity/exclusivity of the candidate method and compare to the FDA/BAM and USDA/FSIS-MLG reference methods as part of the AOAC-RI™ PTM validation.
Methods: The method comparison was conducted on 10 food matrices and 2 environmental surfaces by the candidate method and the reference methods. Each matrix was inoculated with a different strain of both Listeria monocytogenes and Listeria species. 20 replicates were analyzed at one inoculum level: 0.2-2 CFU/25g. Five control replicates were analyzed at 0 CFU/25g. Inclusivity/exclusivity, robustness, stability, product consistency and instrument variation were evaluated.
Results: A POD statistical analysis indicated no significant differences between the new method and the reference methods for Listeria species and L. monocytogenes for all 12 matrices. For inclusivity, 50 out of 50 strains of L. monocytogenes and 10 out of 10 strains each of L. grayi, L. innocua, L. ivanovii, L. seeligeri, and L. welshimeri were correctly identified. All 30 exclusivity organisms were correctly excluded. The robustness results indicated minor variations to testing parameters had no effect on final results. Stability results indicate performance was consistent over the 6 month shelf-life. Product consistency and instrument variation results demonstrated consistency between lots of assay and instruments.
Significance: This new method is a rapid, reliable alternative to the traditional method for simultaneous detection of Listeria monocytogenes and Listeria species.