Performance of the Assurance GDS® Assay for the Detection of L. monocytogenes in Pure Cultures and Spiked Food Samples

Abstract

Listeria monocytogenes is a foodborne pathogen with significant impacts on public health and economy worldwide. Reliable and fast detection of L. monocytogenes is of major importance for both diagnostic laboratories and the food industry. The current study evaluated the performance of the Assurance GDS® assay for the detection of L. monocytogenes in pure cultures and spiked food samples. In the pure culture experiments, the Assurance GDS® assay for Listeria monocytogenes accurately detected the target strains of different serotypes and was correctly negative for a variety of other Listeria species. For reliable detection of L. monocytogenes in pure culture experiments, colony counts >105 cfu/ml were required, which emphasizes the need for an adequate enrichment step. The challenge test experiments (steak tartare, bologna type sausage, Gorgonzola cheese) using a one-broth enrichment strategy showed that the Assurance GDS® assay reliably detected L. monocytogenes after 16 h of enrichment in Half-Fraser broth, provided that spiking levels of the different matrices were ≥102 cfu/g. Depending of the food matrix, longer incubation times of 24 h or 48 h were required when the initial spiking level was <102 cfu/g, as to be expected in a proportion of naturally contaminated food products. Thus, the Assurance GDS® Listeria monocytogenes assay has proven to be a reliable and easy to handle, rapid test system for the specific detection of L. monocytogenes. This system is a suitable tool for generating microbiological results used for a “positive batch release”, especially for RTE foods with short shelf lives. However, longer enrichment times (24 h or 48 h) are required in a one-broth enrichment strategy, when the contamination level of the food matrix is low (<102 cfu/g).