Purpose: The phage-ligand based immunoassay was compared to Assurance GDS® for Listeria spp. (PCR1) and BAX® Genus Listeria 24E (PCR2) for the detection of Listeria in environmental samples and ready-to-eat deli meat.
Methods: Environmental samples (stainless steel, plastic, concrete) and deli ham were inoculated with Listeria spp. (30 replicate samples; 0.2-2 CFU/test portion) and 5 uninoculated controls. All test portions were enriched and analyzed for the detection of Listeria spp. according to manufacturer recommended procedures for the alternative methods and the USDA-FSIS-MLG reference method.
Results: For the combined 90 spiked environmental surfaces, the LPT method detected 42 Listeria positive samples compared to 34 for GDS and 36 for BAX. In the deli-ham, the phage-ligand based immunoassay Listeria method detected 19 Listeria positive samples compared to 13 with PCR1 and 10 for PCR2 out of the 30 inoculated samples. Both POD and chi-squared analysis of these unpaired factional positive samples for the three methods show no statistical difference in recovery.
Significance: The phage-ligand based immunoassay method with single-step enrichment and next day automated detection was statistically equivalent to the PCR1 and PCR2 molecular methods and reference method for detecting Listeria spp. in the environmental and food matrices tested.