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Abstract
In recent years, L. monocytogenes has been frequently implicated in foodborne outbreaks linked to fresh-cut produce. However, little is known about underlying mechanisms of L. monocytogenes transfer and adaptation on fresh-cut produce. We first interviewed three retailers and identified that the common use of gloves represented a potential route for cross contamination with foodborne pathogens. Therefore, we investigated and modeled glove-mediated transfer of L. monocytogenes onto fresh-cut cantaloupe. Then, we characterized transcriptomic responses of L. monocytogenes on fresh-cut apples, cucumbers, cantaloupes, tomatoes, and celery to probe produce factors and bacterial mechanisms that may underlie L. monocytogenes adaptation on fresh-cut produce.Results showed that glove type, contact time, and contact pressure did not have significant effects on L. monocytogenes transfer from cantaloupe rind to flesh or from flesh to flesh. However, glove type appeared to affect L. monocytogenes transfer from the stem scar tissue to cantaloupe flesh (P=0.0371). Transfer from rind pieces that had been washed with water was significantly higher compared to transfer from pieces that had not been washed (P=0.0006). Predictive modeling showed that L. monocytogenes transfer occurs on pieces of cantaloupe flesh sequentially touched 85 times by a gloved hand. With transcriptomic analysis, we identified a core transcriptome including commonly up- and down-regulated genes on fresh-cut produce to explore the factors that may affect the fate of L. monocytogenes on fresh-cut produce. The up-regulated genes are involved in amino acid metabolism, fatty acid metabolism, and membrane transportation. The down-regulated genes are involved in carbohydrate metabolism and transportation. Also, L. monocytogenes was able to make substantial transcriptomic adjustments in response to properties specific to certain produce, such as different abundance of amino acids, carbohydrates, and antimicrobial substance.The study on glove-mediated L. monocytogenes transfer provides insights to conduct risk assessment on the practice used to prepare fresh-cut cantaloupe. Transcriptomic profiling of L. monocytogenes on fresh-cut produce provides molecular assessment of metabolic and stress responses that are likely important for the pathogens adaptation on fresh-cut produce. This study provides potential transcriptomic markers and molecular targets for future development of detection and control strategies of L. monocytogenes on fresh-cut produce.