Environmental monitoring of three fresh-cut processing facilities reveals harborage sites for Listeria monocytogenes

In the present study, the assessment of the environmental contamination by L. monocytogenes was performed after processing, just before cleaning and sanitation processes, in three fresh-cut facilities, including cut vegetables, cut fruits and prepared salads. The main objective was to identify through environmental monitoring (EM) those areas that required extensive investigation as hotspots of contamination. Sites located in Zone 1, Zone 2 and Zone 3 corresponding to food contact surfaces (FCS), close to FCS (within few cm) and remote from FCS (more than 50-100 cm), respectively, were examined. A total of 591 environmental sites were monitored, 204 corresponded to cut vegetables, 177 to cut fruits and 210 to prepared salads. The prevalence of L. monocytogenes and Listeria spp. in the total samples analyzed in all operations was 30% and 40%, respectively. Among facilities, prepared salad showed the greatest L. monocytogenes prevalence (37%, 77/210) followed by the cut vegetables (28%, 56/204) and cut fruit (25%, 45/177). Regarding Zones, L. monocytogenes prevalence was greater in Zone 3 (51%, 135/264), followed by Zone 2 (14%, 18/132) and Zone 1 (13%, 25/195). Some of the sites for L. monocytogenes detection in Zone 1 included the slicers, washing stations, conveyor belts and the vibratory filling while in Zone 3 were linked to drains, floors, ceilings and wheels. Detection of L. monocytogenes was associated with variable Listeria spp. counts (0.3-4 log cfu/unit in Zone 1, 0.2-1.3 log cfu/unit in Zone 2, and 1-4 logs cfu/unit in Zone 3). About 20% of all detected L. monocytogenes samples did not show any cultivable Listeria spp., highlighting the relevance of selecting a method that can detect these species. The data presented in this study emphasized the choice of appropriate detection methods, including pre-enrichment protocol for the sponges combined with filtration. The prevalence of L. monocytogenes in Zone 1 observed in the three processing facilities highlights the need for including FCS in the EM samplings to identify the potential entrance of contamination.