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Identification of Salmonella enterica Genes with a Role in Persistence on Lettuce Leaves During Cold Storage by Recombinase-Based In Vivo Expression Technology

First, third, and seventh authors: Microbial Food-Safety Research Unit, Department of Food Quality & Safety, Institute for Postharvest and Food Sciences, and first author: Department of Biochemistry and Food Science, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot, Israel; second author: Produce Safety and Microbiology Research Unit, United States Department of Agriculture–Agriculture Research Service, Albany, CA; fourth author: Confocal Microscopy Unit, Agricultural Research Organization (ARO), The Volcani Center, Bet Dagan, Israel; and fifth and sixth authors: Department of Plant Pathology & Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.

Recurrent outbreaks of enteric illness linked to lettuce and a lack of efficacious strategies to decontaminate produce underscores the need for a better understanding of the molecular interactions of foodborne pathogens with plants. This study aimed at identifying Salmonella enterica genes involved in the persistence of this organism on post-harvest lettuce during cold storage using recombinase-based in vivo expression technology (RIVET). In total, 37 potentially induced loci were identified in four distinct screenings. Knockout mutations in eight upregulated genes revealed that four of them have a role in persistence of the pathogen in this system. These genes included stfC, bcsA, misL, and yidR, encoding a fimbrial outer membrane usher, a cellulose synthase catalytic subunit, an adhesin of the autotransporter family expressed from the Salmonella pathogenicity island-3, and a putative ATP/GTP-binding protein, respectively. bcsA, misL, and yidR but not stfC mutants were impaired also in attachment and biofilm formation, suggesting that these functions are required for survival of S. enterica on post-harvest lettuce. This is the first report that MisL, which has a role in Salmonella binding to fibronectin in animal hosts, is involved also in adhesion to plant tissue. Hence, our study uncovered a new plant attachment factor in Salmonella and demonstrates that RIVET is an effective approach for investigating human pathogen–plant interactions in a post-harvest leafy vegetable.