MICROBIAL ECOLOGY AND SAFETY OF FRESH PRODUCE

Objective 1. Investigate the mechanism(s) of introduction and transference of Shiga toxigenic E. coli (STEC) and Salmonella to fresh produce during growing, harvest, and postharvest handlings: (1a) Evaluate the growth and survival potential of Enterohemorrhagic E. coli (EHEC) and Salmonella in compost manure applied to leafy green fields and validate cross-contamination and temperature control steps in a Hazard Analysis Critical Control Point (HACCP) system for compost, (1b) Develop a science-based proximity assessment index for airborne bioaerosol emissions for tomato and fresh produce (leafy greens -LG) fields, (1c) Determine the influence of biocontrols and insect amplification and transmission of EHEC and Salmonella in tomato and leafy green crops, and (1d) Evaluate the role of cultivars and fertilization on leafy-green damage during processing and its potential for pathogen contamination. Objective 2. Determine the persistence and survival of pathogens on fresh and fresh-cut leafy green produce: (2a) Determine the persistence of pathogens introduced at different levels on spinach and lettuce plants to verify the adequacy of the California Leafy Greens Marketing Agreement (LGMA), (2b) Identify and evaluate suitable surrogate microorganism for generic E. coli in irrigation water, and (2c) Develop a field-scale-zero valent or slow sand filtration column to inactivate E. coli O157:H12 (surrogate strain) in a field study. Objective 3. Determine the effects of pathogen attachment, biofilm formation, and internalization on the extent of contamination of fresh produce: (3a) Determine the role of various virulence and stress factors on the ability of EHEC to persist on leafy green surfaces, and (3b) Determine the effect of biofilm formation on survival of STEC and Salmonella on fresh produce. Objective 4: Develop effective intervention technologies during processing to inactivate pathogens, and/or to reduce their survival and growth while maintaining produce quality and shelf-life: (4a) Minimizing pathogen transference and infiltration during produce harvesting and post-harvest handling, (4b) Optimizing fresh-cut produce wash system configurations and operations to improve pathogen inactivation and minimize cross-contamination, and (4c) Effect of temperature and packaging atmospheric conditions on survival, growth, and virulence of EHEC.