A Comparative Evaluation for Listeria Species in Food with the Roka Listeria Detection Assay on Atlas™ System vs. DuPont Qualicon's BAX® System 24E Assay

Introduction: Listeria is an environmentally ubiquitous organism implicated as a major cause of human foodborne illness worldwide. Listeria’slong lag phase and hindered growth in the presence of competitive flora presents a challenge for rapid and reliable detection with a single 24-hour enrichment step.

Purpose: Compare the detection and assay efficiency of Listeria monocytogenes in inoculated foods after 24-28 hour enrichment with the Roka Bioscience Listeria Detection Assay on Atlas™ System vs. DuPont Qualicon’s BAX® System PCR 24E Assay.

Methods:   Five foods are assessed: 1) hummus, 2) cantaloupe, 3) frozen waffle, 4) fresh mozzarella, and 5) deli turkey. Five non-inoculated and 20 inoculated samples are tested and compared to culture. For the Roka assay, Half-Fraser is added, incubated at 35°C for 24-28 hours, a sample transferred to a collection tube containing a lysis reagent, and tested on Atlas™ System. For the BAX assay, 24 LEB is added, incubated at 37°C for 24-28 hours, a sample transferred to cluster tubes for a two-part lysis procedure, a PCR tablet is hydrated with lysate, and tested on BAX. Post enrichment enumeration on MOX agar is determined with discrepant analysis utilizing motility and catalase tests.

Results: The Roka assay demonstrates 100% sensitivity and specificity for all five foods compared to culture. The BAX assay demonstrates in hummus and fresh mozzarella 100% sensitivity and specificity, in cantaloupe 93.3% sensitivity and 73.3% specificity, in frozen waffle 100% sensitivity and 78.9% specificity, and in deli turkey 100% sensitivity and 93.8% specificity.

Significance: The Roka assay demonstrates improved sensitivity and specificity compared to the BAX assay in cantaloupe, frozen waffles, deli turkey, and comparable results in hummus and fresh mozzarella after 24-28 hours of enrichment.