Purpose: The study was conducted according to the AOAC-RI Performance Test MethodSM validation process to evaluate the Assay for use with a representative range of produce, meat, dairy and sea-food matrices as well as stainless steel surfaces.
Methods: Validation of the SureTect Listeria monocytogenes Assay was conducted by enriching 25g samples of food matrices or surface sponges in supplemented OxoidTM 24 LEB Broth for 22 hours, followed by PCR analysis according to SureTect method instructions. Cooked deli-ham, smoked salmon, salami, prawns, raw cod, ice-cream, American style cheese, Brie, fresh spinach & lettuce, cantaloupe melon, Frankfurters & stainless steel surfaces were evaluated in comparison to the ISO 11290-1:1998, Amd 1:2004 reference method. Foods were spiked at low (0.2-2 CFU/25g) and high (2-5 CFU/25g) levels, with low level spiking required to achieve fractional positive rates across 20 replicate samples. All PCR positive results were confirmed using the SureTect confirmation protocol (plating onto BrillianceTM Listeria Agar) and by a shortened ISO confirmation procedure.
Results: Internal and external independent validation demonstrated that the Assay gave equivalent or better performance than ISO 11290-1 for all matrices studied. Results from the Assay were in agreement by probability of detection statistical analysis with ISO 11290-1. When compared with the reference method, the mean RLOD for all matrices was 0.705 CFU/25g (0.037-1.427). Inclusivity testing detected all of 53 isolates of L. monocytogenes tested. None of the 38 exclusivity isolates were detected by the assay.
Significance: The PCR assay was shown to be an accurate and user-friendly method, due to the use of pre-dispensed lysis reagent, tableted PCR reagents and automatic interpretation of results. Results for a wide range of foods, including challenging matrices, demonstrated the assay was able to reliably detect the presence of L. monocytogenes.