L. monocytogenes growth potential, kinetics, and factors affecting its persistence on a broad range of fresh produce

Listeria monocytogenes (Lm) is a major foodborne pathogen that has been characterized as ubiquitously present in the natural and food production environments, and has been implicated in multiple fresh produce related listeriosis outbreaks. Although a mesophilic bacterium, its ability of growth under refrigeration makes Lm an especially dangerous contaminant for vulnerable ready to eat (RTE) foods, including fresh-cut fruits and vegetables. Lm is also known for deficiencies in the synthesis of multiple vitamins and amino acids and sensitivity to high acidity. Therefore, Lm growth potential on given fresh produce is dependent of produce intrinsic characteristics and environmental factors. Research outlined in this proposal is aimed at addressing CPS 2018 RFP Research Priorities 1.1.5: Expanding knowledge on Listeria growth potential and kinetics; and 2.3.3: Factors affecting human pathogen persistence. The objectives of this research are: 1) to assess Lm growth potentials on a broad range of fresh fruits and vegetable under simulated normal storage and retail display conditions; 2) to examine temperature abuse on Lm growth potentials on selected whole and fresh-cut produce and develop a Lm growth potential-based means for quantifying temperature abuse; 3) to investigate produce intrinsic characteristics, including nutrient (specifically, vitamins and amino acids required for Lm growth), acidity, and potential anti-listerial substances, on Lm growth potentials, and 4) to explore the potential role of produce microbiota on Lm growth and persistence on fresh produce. A large variety of whole and fresh-cut fruits and vegetables representing multiple produce categories will be selected for testing in consideration of multiple factors including means of consumption, market volume, and typical storage/display conditions. Lm growth potential and kinetics will be determined using conventional microbiological analyses by inoculation multiple Lm strains on whole and fresh cut fruits and vegetables, and enumerating the surviving or grown Lm cells at time intervals appropriate for the storage conditions. Uninoculated controls will be used for assessing the behaviors of produce microbiota under the same conditions. Produce quality assessment will be conducted in parallel to microbiological analyses to make sure that the data is relevant to industry practices. Lm growth potentials and kinetics and the effects of produce intrinsic characteristics will also be determined using diluted sterile extracts from relevant fresh-cut produce. Produce microbiome shifts during storage/display will be determined using 16S rDNA survey-based metagenomic analyses. Effectively managing Lm food safety risks is a high priority for both fresh produce industry and regulatory agencies. Recent FDA draft guidelines for Lm risk management recommended different industrial actions based on commodity-specific assessment of Lm growth potentials. Information from this proposed research can be of great importance to both fresh produce industry and regulatory agencies for developing commodity specific guidelines and practices to minimize the food safety risks resulted from Lm contamination and growth on fresh produce.