Interactions of Salmonella enterica with lettuce leaves

Authors

  • Y. Kroupitski,

    1.  Microbial Food-Safety Research Unit, Department of Food Science, Institute for Technology and Storage of Fresh Produce, Agricultural Research Organization (ARO), The Volcani Center, Beth-Dagan, Israel
    2.  Department of Human Microbiology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel
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  • R. Pinto,

    1.  Microbial Food-Safety Research Unit, Department of Food Science, Institute for Technology and Storage of Fresh Produce, Agricultural Research Organization (ARO), The Volcani Center, Beth-Dagan, Israel
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  • M.T. Brandl,

    1.  Produce Safety and Microbiology Research Unit, US Department of Agriculture, Agriculture Research Center, Albany, CA, USA
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  • E. Belausov,

    1.  Confocal Microscopy Unit, Agricultural Research Organization (ARO), The Volcani Center, Beth-Dagan, Israel
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  • S. Sela

    1.  Microbial Food-Safety Research Unit, Department of Food Science, Institute for Technology and Storage of Fresh Produce, Agricultural Research Organization (ARO), The Volcani Center, Beth-Dagan, Israel
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Shlomo Sela, Microbial Food-Safety Research Unit, Department of Food Science, Agricultural Research Organization (ARO), The Volcani Center, POB 6, Beth-Dagan 50250, Israel. E-mail: shlomos@volcani.agri.gov.il

Abstract

Aims:  To investigate the interactions of Salmonella enterica with abiotic and plant surfaces and their effect on the tolerance of the pathogen to various stressors.

Methods and Results: Salmonella strains were tested for their ability to form biofilm in various growth media using a polystyrene plate model. Strong biofilm producers were found to attach better to intact Romaine lettuce leaf tissue compared to weak producers. Confocal microscopy and viable count studies revealed preferential attachment of Salmonella to cut-regions of the leaf after 2 h at 25°C, but not for 18 h at 4°C. Storage of intact lettuce pieces contaminated with Salmonella for 9 days at 4°C resulted only in small changes in population size. Exposure of lettuce-associated Salmonella cells to acidic conditions (pH 3·0) revealed increased tolerance of the attached vs planktonic bacteria.

Conclusions:  Biofilm formation on polystyrene may provide a suitable model to predict the initial interaction of Salmonella with cut Romaine lettuce leaves. Association of the pathogen with lettuce leaves facilitates its persistence during storage and enhances its acid tolerance.

Significance and Impact of the Study:  Understanding the interactions between foodborne pathogens and lettuce might be useful in developing new approaches to prevent fresh produce-associated outbreaks.

Ancillary