Efficacy of Environmental Sampling Devices for Listeria monocytogenes Detection in a Ready-to-Eat Production Facility

Listeria monocytogenes is considered a highly persistent risk for public health in food production facilities. Food business operators manufacturing ready-to-eat foods (RTE) are required to sample processing areas for L. monocytogenes as part of their environmental monitoring plans. The aim of the study was to identify suitable sampling devices, demonstrating the crucial role of the sampling technique in the method performance for L. monocytogenes monitoring. Detection of Listeria spp. and L. monocytogenes from surfaces in an RTE food production facility was evaluated by using two different sampling methods (swabs and sponges). When using swabs, 46 sampling points were negative for both targets. However, when sampling same points with sponges, 30% samples (14 out of 46) were positive for Listeria spp. with 8 samples (17%) positive for L. monocytogenes. During subsequent in vitro experiments, L. monocytogenes strains spiked onto three different surfaces (stainless steel, Teflon and epoxy) showed recoveries of between 76% and 93% when using sponges, while in swabs, recoveries where always below 50%. All L. monocytogenes strains isolated belonged to the major clonal complexes (CC) circulating in Europe in food industry (e.g., CC121 and CC9) and none of them are considered among the hypervirulent strains. Genomic analysis, including new tools for source tracking (Gene Up Typer, bioMérieux) showed differences between strains isolated from different risk hygienic zones.