Listeria monocytogenes in the retail deli environment: A review

Listeria monocytogenes has long been associated with ready-to-eat foods, particularly with deli products. A retail deli is full of potential niches for L. monocytogenes to establish, and this poses a significant sanitation challenge. Retail sliced deli meat products, also known as luncheon meat or cold cuts, are subject to long home storage times under refrigerated conditions where L. monocytogenes can multiply; these commonly consumed ready-to-eat meats are high risk for getting cross-contaminated in the retail deli environment and causing listeriosis. This review considers elements of the retail deli environment which can affect the prevalence and persistence of L. monocytogenes that may lead to contamination of sliced meat, as well as the specific attributes associated with L. monocytogenes isolated from deli environments and decontamination measures assessed to reduce L. monocytogenes prevalence in deli environments. In deli environments, the ratio of L. monocytogenes to Listeria spp. is 2.4:1, and L. monocytogenes is found twice as frequently on non-food contact surfaces compared to food contact surfaces. Elements that may affect the likelihood of this pathogen persisting in the deli environment are sanitizer tolerance and biofilm formation ability; it is found that there are no differences in sanitizer tolerance between transient and persistent deli strains, but biofilm formation is a trait linked to persistence in L. monocytogenes isolated from delis. A major virulence factor in L. monocytogenes, full length internalin gene inlA, has a higher prevalence in retail deli isolates compared to the studied prevalence in all food isolatesbut closely resembles the prevalence in clinical isolates, suggesting that the retail deli is a major source of clinically recognized listeriosis cases. To combat this pathogen, the merits of daily intervention as well as deep cleans are discussed; increased employee commitment to cleaning programs and a greater food safety culture are related to improved retail deli cleanliness. •Isolates from delis, like clinical isolates, rarely have inlA virulence-reducing mutations.•L. monocytogenes is twice as common on non-food contact surfaces in delis as on food contact surfaces.•Isolates from food contact surfaces in delis are more often lineage II than non-food contact isolates.•Stress survival islet-1 correlates with high biofilm formation, persistence in food manufacturing.•Persistent lineage II L. monocytogenes food isolates