Evaluation of the 3M™ Molecular Detection Assay (MDA) Listeria (LS) and Listeria monocytogenes (LM) for the Detection of Listeria in a Variety of Foods: Collaborative Study

Introduction: The 3M Molecular Detection Assay (MDA) Listeria (LS) and Listeria monocytogenes (LM) methods use loop-mediated isothermal amplification of nucleic acid sequences to detect Listeria in enriched food and environmental samples. The isothermal amplification is a polymerase chain reaction conducted at a constant temperature, eliminating the need for temperature cycling and decreasing the time-to-results. The new methods employ unique DNA target sequences with high specificity and efficiency to detect target pathogens in 24 - 30 hours of enrichment.  

Purpose: The purpose of this AOAC^®OMA℠ Collaborative Study was to compare the new methods to the USDA-FSIS/MLG for deli turkey (125 g) (MDA LM only) and the AOAC OMA 993.12 for full fat cottage cheese (25 g) (MDA LS and MDA LM).

Methods: The two rapid methods were compared in a multi-laboratory collaborative study to the USDA-FSIS MLG Chapter 8.09 and to the AOAC OMA 993.12 reference methods. A total of 17 laboratories, representing government and industry, throughout the United States and Canada participated.  Each laboratory evaluated 12 replicates at 3 levels of inoculation; an un-inoculated control level (0 CFU/test portion), a low inoculum level (0.2 - 2 CFU/test portion) and a high inoculum level (2 - 5 CFU/test portion).  All test portions were confirmed using the appropriate reference method.

Results: Statistical analysis was conducted according to the Probability of Detection (POD) statistical model.  No statistically significant difference was observed between the new and reference methods.  The new Listeria method correctly identified whether a test portion was positive or negative more than 99.2% of the time.  The new L. monocytogenes method correctly identified whether a test portion was positive or negative more than 98.1% of the time.

Significance: The collaborative study demonstrated the reliability and sensitivity of these new methods for the rapid detection of Listeria in food products using both 125 g and 25 g sample test portion sizes.