Comparison of 3M™ Molecular Detection Assay (MDA) Listeria monocytogenes with ISO Standard Method for Rapid Detection of L. monocytogenes Artificially Inoculated on Food Contact Surfaces with or without Organic Load

Introduction: Food contact surfaces contaminated with L. monocytogenes is an important issue for Ready-to-Eat food manufacturers, since surfaces could be a major source of reoccurrence of Listeriosis. It is crucial to implement rapid detection methods at the factory to control such Listeriosis. A commercial rapid detection system based on loop-mediated isothermal amplification coupled with bioluminescence has been developed, and requires broader validation with food contact surfaces in detecting L. monocytogenes.

Purpose: This study aims to evaluate the performance of 3M Molecular Detection System (MDS) in comparison with ISO method for detection of L. monocytogenes on stainless steel and polyethylene surfaces artificially inoculated at low levels with or without organic load.

Methods: The 3-strain cocktail of L. monocytogenes was inoculated on stainless steel and polyethylene surfaces (10 x 10 cm) to achieve 10⁰, 10¹ and 10² CFU/100 cm². To prepare the surface with organic load, fresh raw salmon was homogenized with peptone water and the suspension was spread evenly across the surface prior to inoculation. A total of 120 samples were subjected to both MDS and ISO methods. 

Results: The MDS method performed equally effectively compared with ISO method at inoculum levels of 10⁰ and 10²/100 cm², on both surfaces. Reported sensitivity and specificity for inoculum at 10¹ CFU/100 cm² were more than 80%, except for stainless steel surfaces without organic load that had a reported sensitivity and specificity of 75% and 92%, respectively.

Significance: This study demonstrates that MDS can provide cost effective, rapid and accurate detection of L. monocytogenes at low inoculum levels on stainless steel and polyethylene surfaces in 26 - 30 hours with a single enrichment.