Purpose: To demonstrate the equivalence of Assurance GDS for both Listeria spp. and Listeria monocytogenes Tq to the reference culture method for the detection of L. monocytogenes in fish and seafood products.
Methods: Four food matrices from the fish and seafood category representing smoked fish (smoked salmon), frozen fish (fish sticks), raw fish (cod fillets) and heat processed fish (canned tuna) were included in the study. For heat processed fish, 40 samples were inoculated with low levels of L. monocytogenes, 40 samples were inoculated with high levels of L. monocytogenes and 10 uninoculated samples were included as controls. For frozen and raw fish, 20 samples were inoculated with low levels of L. monocytogenes, 20 samples were inoculated with high levels of L. monocytogenes and 5 uninoculated samples were included as controls. 25-g test portions of heat processed and raw fish were enriched in 225 ml Buffered Listeria Enrichment Broth with Lithium Chloride and PALCAM supplement for 18 hours at 35-37°C. A 1 ml aliquot of the enrichment was transferred to 30°C an additional 6 hours. For frozen fish, 25-g test portions were enriched in 225 ml of Demi Fraser Broth for 22 hours at 30°C. All samples were analyzed using a novel method for detecting both Listeria spp. and Listeria monocytogenes according to the directions for use and reference culture methods. For all samples, the reference method used was Health Canada MFHPB-30.
Results: A total of 135 samples were analyzed for Listeria spp. a total of 180 samples were analyzed for Listeria monocytogenes. A probability of detection (POD) analysis showed that for all matrices, the performance of Assurance GDS for both Listeria spp. and Listeria monocytogenes Tq weres equivalent to the reference culture method.
Significance: This new detection method for fish and seafood provides the industry with a faster option for testing for both Listeria spp. and Listeria monocytogenes than culture methods, while retaining the necessary accuracy.