Characteristics and practices that may lead to Listeria monocytogenes contamination in retail delis

The foodborne pathogen, Listeria monocytogenes, can contaminate ready-to-eat (RTE) deli meats at retail delis, since retail delis provide an ideal environment for L. monocytogenes growth. Current risk assessment indicates that 83% of listeriosis cases from RTE deli meats are all from RTE deli that are sliced at retail delis. Strategies for controlling L. monocytogenes in retail establishments are essential to prevent post-processing contamination of RTE foods. In order to determine the potential risk factors associated with L. monocytogenes contamination and develop best practices to reduce L. monocytogenes , we sampled the retail establishment environment, isolated L. monocytogenes, and conducted a Store Characteristics Survey analysis among 85 retail deli establishments. L. monocytogenes prevalence was higher on non-food contact than food contact surfaces. Several practices implemented in retail delis were shown to be risk factors for L. monocytogenes cross-contamination. For example, handling raw meat near deli area, low numbers of slicers designated to slice deli meats, and all sanitizers not properly applied were associated with high L. monocytogenes prevalence (p \u3c 0.05). In addition, the intrinsic factors of L. monocytogenes have also been linked to cross-contamination in retail deli establishments. Studies have shown that L. monocytogenes can persist in a deli environment for a long time and can cross-contaminate foods when cleaning and sanitizing are not properly executed. To understand the correlation between L. monocytogenes persistence and biofilm formation as well as sanitizer tolerance, we assessed sanitizer tolerance to quaternary ammonia by minimum inhibitory concentration (MIC) and biofilm formation by attachment assay among 41 persistent and 97 transient isolates. Persistent L. monocytogenes isolates were more likely to form biofilms and tolerate to sanitizer (p \u3c0.05) than transient isolates. A negative correlation was detected between isolates with enhanced biofilm formation on day 5 and sanitizer tolerance, meaning week biofilm formation might result in higher sanitizer tolerance. Data obtained from this study underscores the importance of appropriate cleaning, sanitation, and hygiene programs, as well as food safety education. Additionally, we provided insight into contributing factors that may support L. monocytogenes persistence in retail establishment environment