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Abstract
Listeria monocytogenes has been increasingly linked to fresh produce-related recalls and outbreaks. Additionally, the prevalence of Listeria species and L. monocytogenes has not been well characterized throughout each stage of the fresh produce supply chain. Fresh produce is typically contained and shipped within vented packaging to maintain product quality, which may offer a potential route of contamination. Therefore, this study addressed Listeria prevalence across the fresh produce supply chain, with a primary focus on the distribution center environment. The first objective of this study was to determine research gaps regarding Listeria species along the fresh produce supply chain through a systematic literature review. This review identified 64 relevant articles examining Listeria species and L. monocytogenes prevalence, persistence, and diversity across natural environments and outdoor production, packinghouse, indoor production and processing, retail, farmers’ markets, and domestic environments. The greatest prevalence of Listeria species and L. monocytogenes was found in natural environments and outdoor production. Research gaps were identified at the transportation and distribution center stage. The second objective was to determine the prevalence of Listeria species in distribution centers (n = 18) handling fresh produce. Relationships between detection of Listeria species within these centers and environmental factors (e.g., temperature, relative humidity, cleaning regimen) were also investigated. Listeria was isolated from 49 out of 982 (ca. 5%) environmental surface swabs; however, Listeria was not isolated from impaction air samples (n = 170). Several variables, such as individual distribution center, sampling location, season, and geography, were significantly associated with Listeria detection. A random forest model determined geographical location and general sampling location as the two most important variables associated with Listeria detection. The final objective was to characterize microbial communities within these distribution centers using 16S amplicon sequencing. Two bioinformatics workflows were used to analyze the 1) Listeria-targeted microbiome and the 2) overall microbiome from 317 surface swabs. Amplicon sequencing reads containing Listeria ASVs out of all reads had a relatively low prevalence of ca. 4%. Microbiome composition appeared to vary significantly across groupings within variables (e.g., DC, season, general sampling location).