Comparative evaluation of 14 hlyA-based loop-mediated isothermal amplification assays for the rapid detection of Listeria monocytogenes.

INTRODUCTION: Rapid detection of Listeria monocytogenes in food is critical for implementing timely measures to reduce foodborne listeriosis and subsequent fatalities. While multiple L. monocytogenes loop-mediated isothermal amplification (LAMP) assays targeting the hlyA gene (listeriolysin O) have been reported in the literature, no independent comparative evaluation has been conducted. METHODS: In this work, we evaluated the performance of 14 hlyA-based L. monocytogenes LAMP assays, using an FDA-developed L. monocytogenes LAMP assay targeting the same gene for benchmarking. All assays were performed in an enclosed OptiGene Genie II platform using a harmonized protocol (not individually reported/optimized conditions). The assay sensitivity (limit of detection, LOD) and specificity (inclusivity/exclusivity) were determined using a ten-fold serially diluted reference L. monocytogenes culture (ATCC 19115), and a panel of 50 L. monocytogenes strains, 20 other Listeria spp. strains, and 31 non-Listeria strains, respectively. We also evaluated the quantification capabilities of these LAMP assays. RESULTS AND DISCUSSION: The LODs for these 14 LAMP assays using L. monocytogenes ATCC 19115 ranged from exceeding 106 cells per reaction (i.e., nondetectable for three of them at the highest concentration tested) to 102 cells per reaction, with the latter including the FDA LAMP assay. The inclusivity ranged from 20 to 90% detection using the initial templates prepared at approximately 100-102 cells per reaction whereas 100% inclusivity was observed for two selected and the FDA LAMP assays at higher template concentrations. All 14 assays had 100% exclusivity. The quantification capabilities of these assays varied with correlation coefficients ranging from 0.681 to 0.992. This comprehensive evaluation of 14 hlyA-based L. monocytogenes LAMP assays highlights the critical role of assay design in enabling rapid, sensitive, and specific detection of this prominent foodborne pathogen to ensure food safety and protect public health.