Purpose: The purpose of this study was to determine the prevalence of L. monocytogenes and S. enterica in retail produce environments and to elucidate possible ecological niches.
Methods: Thirty environmental samples were collected monthly for six months, in duplicate, in 30 retail produce departments in seven states during daily operation. Samples included 17 food contact surfaces and 13 nonfood contact surfaces. Each sample was tested for L. monocytogenes and S. enterica using ROKA Atlas LmG2 and SEN assays, respectively. Positive L. monocytogenes enrichments were confirmed by secondary enrichment in Fraser broth and plating; positive S. enterica enrichments were confirmed using the standard FDA BAM protocol.
Results: A total of 4.4% (226 of 5,112) of environmental samples tested positive for L. monocytogenes. Listeria monocytogenes was present on 8.1% (178 of 2,205) nonfood contact surfaces and 1.6% (48 of 2907) of food contact surfaces tested. Seven of 30 stores showed low overall L. monocytogenes prevalence across all sites (<1%) and four of 30 stores had high overall prevalence (>10%). The majority of positive L. monocytogenes samples were found on the drains or floors, squeegees, and in standing water. Salmonella enterica was found during one sampling event in a single store; <0.1% (four of 5,112) of samples were positive overall.
Significance: This study suggested that retail environments may be a significant source of L. monocytogenes, which may result in cross-contamination to produce. However, the data indicated that S. enterica prevalence, in retail, is very low and likely due to transient contamination events.