Listeria monocytogenes is prevalent in retail produce environments but Salmonella enterica is rare

摘要

The purpose of this study was to determine the prevalence of Listeria monocytogenes and Salmonella enterica in retail produce environments and to elucidate possible ecological niches. Thirty environmental samples per store were collected during daily operations monthly for six months in 30 retail produce departments across seven states. Selected samples were serially diluted and plated to determine aerobic plate count. Each sample was tested for L. monocytogenes and S. enterica using ROKA Atlas LmG2 and SEN assays, respectively. A total of 5,112 samples were tested for each pathogen. S. enterica was found during one sampling event in a single store; less than 0.1% of samples were positive overall. A total of 4.4% environmental samples tested positive for L. monocytogenes. L. monocytogenes was present on 8.1% of non-food contact surfaces and 1.6% of food contact surfaces tested; L. monocytogenes prevalence was highly variable among stores. Most of the positive L. monocytogenes samples were found in drains, floors, squeegees, or standing water. Genetically similar L. monocytogenes clones were found in multiple stores across multiple states. The odds of detecting L. monocytogenes increased 1.8-fold for every 1-log increase in APC (p < 0.0001). This is the first study to investigate prevalence and persistence of L. monocytogenes and S. enterica in retail produce environments. Our data suggest that some, but not all retail produce environments have high L. monocytogenes prevalence, which may cross-contaminate produce. Sites heavily contaminated with L. monocytogenes indicate potential targets for sanitation operating procedures and food safety management strategies. However, S. enterica prevalence is very low and likely due to transient contamination. Further, APC may be a cost-effective environmental monitoring tool that could indicate an environment capable of harboring L. monocytogenes.