Purpose: To evaluate the Roka Listeria Detection Assay system for the detection of Listeria spp. in food and environmental surfaces in an AOAC Research Institute Performance Testing Methods (PTM) study utilizing Roka’s high throughput, fully automated walk-away instrument – AtlasTM System.
Methods: The method includes 24-28 hours enrichment at 35°C for foods and environmental surfaces in Half-Fraser media. Enriched sample is transferred to a collection tube containing lysis reagent and loaded onto the Atlas™instrument where template-specific sample extraction, TMA amplification, probe detection and analysis of the results are all performed. A total of 9 foods and 3 environmental surface matrices are compared to a cultural reference method in an internal study, as well as, 2 foods and 1 environmental surface in an external study. Selectivity was evaluated by testing 50 target microorganisms and 30 non-target microorganisms.
Results: The test method provided a positive result for 100% of 50 target microorganisms, and a negative result for all 30 non-target microorganisms commonly found in food and grown to a titer > 1+E08 CFU/ml. No significant differences were observed between the Roka Listeria Detection Assay and the cultural reference methods for cured ham, chicken salad, deli chicken, brie cheese, pasteurized whole milk, cold smoked salmon, romaine lettuce, hot dog inoculated with L. grayi, stainless steel and sealed concrete. Significant differences were observed with Roka’s method demonstrating higher sensitivity to detect positives in vanilla ice cream, PVC plastic and hot dog inoculated with L. innocua.
Significance: Roka’s method provides final negative or presumptive positive results in 24-28 hours compared to at least 3 days for culture methods. Listeria spp. can be detected at low levels of contamination and combined with the AtlasTM System offers a rapid, specific, and user-friendly test method to monitor and limit contamination issues.