Purpose: The purpose of this internal validation was to evaluate the ruggedness, product consistency, stability, instrument variation and inclusivity/exclusivity of the candidate method and compare it to the FDA/BAM and USDA/FSIS-MLG biochemical confirmation process as part of the AOAC-RI™ PTM validation.
Methods: A method comparison of 10 food matrices and 2 environmental surfaces was conducted using the GeneDisc® Plate Listeria ID and the FDA/BAM or USDA/FSIS-MLG reference methods. For confirmation of samples by the ID method, each matrix was streaked to 6 different agars (MOX, OX OAA, Palcam, Rapid‘L.mono™ and Nutrient Agar). Typical Listeria colonies from each agar were picked for identification by the candidate method. Inclusivity/exclusivity, stability, product consistency and instrument variation parameters were evaluated.
Results: For the method comparison, the candidate method correctly identified 722 out of 727 isolates (99.3%). For inclusivity, 837 out of 840 isolates (99.6%) 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 demonstrate consistency between lots of assay and instruments.
Significance: The candidate method demonstrated high specificity in the identification and discrimination of Listeria species.