Purpose: The purpose of this evaluation was to conduct a comparison of the new method to the FDA, USDA or OMA reference methods for the detection of Listeria spp. or L. monocytogenes in selected foods and environmental surfaces as part of the AOAC-RI™ PTM validation process.
Methods: The method comparison analyzed 10 matrices: hot dogs, deli turkey, smoked salmon, mung bean sprouts, pasteurized whole milk, Gouda cheese and stainless steel, ceramic tile, plastic, and sealed concrete in an unpaired study. Matrices were co-inoculated at two levels (0.2-2 CFU/25g and 2-5 CFU/25g) with a different strain of L. monocytogenes and Listeria spp. For each matrix, Oxoid Novel Enrichment Broth (ONE Broth) plus ONE Broth Selective Supplement was validated. DNA was extracted using both the manual mericon™ DNA Bacteria Kit or the automated QIAsymphony mericon™ Bacteria Kit, analyzed by the RotorGene real-time PCR system for Listeria spp. or L. monocytogenes and compared to the appropriate reference method. Test kits were also evaluated for ruggedness, inclusivity and exclusivity.
Results: The method comparison demonstrated no statistically significant differences (POD statistical model) in the number of positive samples detected by the mericon candidate methods and the reference methods for all 10 matrices studied. All 50 inclusivity strains were detected. None of the 30 non-target exclusivity strains was detected. The ruggedness evaluation indicated that minor modifications in the procedure did not affect the outcome
Significance: This new method is an efficient and reliable alternative to traditional reference methods for detecting Listeria species and L. monocytogenes in selected foods and environmental samples.