Mitigating Prevalence and Persistence of L. monocytogenes using Novel Sanitation Strategies in Delis

Susan Rose Hammons, Purdue University


Ready-to-eat (RTE) deli meats sliced at retail are predicted to cause 83% of deli meat-associated listeriosis cases annually. While L. monocytogenes is commonly found in delis (55-90%), environmental prevalence varies by store (0-40%). Study 1 evaluated efficacy of 10 standardized SSOPs by testing 28 food and non-food contact surfaces for L. monocytogenes over 6 months in 30 retail delis. Intervention strategies employed in this study significantly decreased L. monocytogenes prevalence on FCS and NFCS in stores with moderate prevalence (0.5%, 0.8% reduction). However, we found that L. monocytogenes could persist despite implementation of SSOP control strategies. Study 2 assessed an aggressive 12 hour deep clean sanitation standard operating procedure (SSOP) in nine retail delis aimed to reduce persistent Listeria monocytogenes. The SSOP was executed by a trained professional cleaning service during a 12 hour shut-down. Delis (n=5) with historically low L. monocytogenes prevalence (<1% samples; >300 samples tested) had no statistically significant changes in L. monocytogenes positive samples after the deep clean. In two delis with historically high L. monocytogenes prevalence (>10%), deep cleaning reduced L. monocytogenes positive samples by 50% and 75%; one deli had no change and one store had increased L. monocytogenes positive samples immediately post-deep clean. High prevalence delis returned to pre-deep clean L. monocytogenes prevalence levels within one month. Study 3 assessed the efficacy of a modified deep-clean SSOP conducted by store employees and complemented with training and facilities improvements to reduce L. monocytogenes prevalence. Fifty delis among 6 states were screened using a predictive logistic regression model that estimates the probability of high L. monocytogenes prevalence in a deli. Environmental samples (n=20) were collected immediately before, after, and once monthly for 6 months post-deep clean. Deep-cleans immediately reduced L. monocytogenes prevalence in 6 of 7 stores tested. A total of 22/139 (15.8%) samples before and 8/140 (5.7%) samples after deep-cleaning were positive for L. monocytogenes, a marginal mean decrease of 10.1 percentage points (CI95: -0.01, 21.0%; p=0.066) per store. Interventions reduced average monthly L. monocytogenes prevalence in each store by 9.7 percentage points (CI95: 2.50, 16.9%; p=0.017). Employee executed deep-cleans with training, education, and maintenance programs can reduce environmental L. monocytogenes prevalence, a pivotal part of preventing cross-contamination to RTE deli meats. Taken together, these studies underscore that improved sanitation strategies combined with facilities maintenance and improving food safety culture are pivotal to preventing listeriosis from RTE deli meats contaminated at retail.




Oliver, Purdue University.

Subject Area

Food Science|Microbiology

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