Survival of Listeria monocytogenes and Salmonella on surfaces found in the dry packinghouse environment and effectiveness of dry-cleaning processes on pathogen reduction

The percentage of produce commodities contaminated with foodborne pathogens has increased in the past decade. These products are often consumed raw or with minimal processing or preparation, which contributes to the risk of food-borne disease. Salmonella and Listeria monocytogenes are two bacterial foodborne pathogens of concern for the produce industry. A packing company issued in 2016 the first recall of certain stone fruits because of concern about contamination with Listeria monocytogenes. Another 2020 interstate recall of peaches involved contamination with Salmonella. Additionally, Salmonella and L. monocytogenes are significant pathogens for other commodities such as leafy greens, tomatoes, cantaloups and mango. In the absence of any practices that prevent pathogen survival on the product, the exposure of the fresh produce to contaminated postharvest contact surfaces will increase the likelihood of contamination and foodborne outbreaks. In certain areas of the packinghouse, FSMA grants the use of dry cleaning techniques such as vacuuming or scrapping followed by the use of dry sanitizers for food contact surfaces, or Zone 1 areas. The use or presence of water could be a significant risk for foodborne pathogen growth, cross-contamination, and dissemination in the facility. However, microorganisms have multiple mechanisms for microbial adaptation and survival in dry conditions. Microbial survival in low moisture and desiccation conditions present in the packinghouse can lead to cross-contamination. In addition, adverse dry conditions could force bacteria to enter an inactive physiological state, such as viable but nonculturable (VBNC). The presence of VBNC cells has food safety implications since these microorganisms may be undetected during routine sampling for environmental monitoring. In the proposed research we aim to determine survival of dry surface-associated planktonic and biofilms of L. monocytogenes and Salmonella grown in combination with background microflora on surfaces typically found in the packinghouse. In Objective 1, pathogen die off rates will be determined for mixed planktonic and biofilms dried on packinghouse surfaces. Multiple analytical methods of analysis (plate count, microscopy, real-time PCFR) for the dry films will avoid false negative results (e.g., low number in the mixed film and possibly injured cells that are not recovered for the quantification assay) and determine the effects of matric stress on the formation of VBNC microorganisms. Experiments will investigate the conditions that favor transition of the planktonic cells present on surfaces to form attached embedded communities or biofilms (the main question is when and how a dried cell becomes embedded biofilm). Inactivation studies in Objective 2 will provide data for best practices regarding dry cleaning/sanitation methodology in the packing house and elimination of the foodborne pathogens. Objective 3, a pilot plant study, will validate findings from Objectives 1 and 2 for practical use in the packing house, to reduce the load of microorganisms on equipment and produce. Together the laboratory data and pilot plant trials can identify management practices associated with reduced pathogen presence in the dry environment. This project is intended for CPS 2021 Research Priorities-Part 3a. Packing, Cooling and Storage.