1a. Objectives (from AD-416)
The overall goal of this research is to reduce the occurrence, risk, and severity of illness associated with consumption of foods contaminated with pathogenic microorganisms. This project will focus on the following three main objectives aimed at increasing our understanding of pathogen persistence in foods and, in turn, developing and evaluating effective interventions to enhance the safety and security of our food supply: 1. Determine the prevalence, levels, types, and locations of pathogens at various points from production through to consumption of raw, further processed, and/or RTE foods. 1.1. Determine the prevalence of L. monocytogenes in retail environments to include harborage sites, mechanisms of cross-contamination, and external sources of contamination. 1.2. Determine the relatedness of L. monocytogenes from FSIS- and FDA-regulated foods using molecular typing methods such as PFGE and MLGT. 2. Develop, optimize, and validate processing technologies for eliminating pathogens. 2.1. Determine the transfer and survival of Shiga-toxin producing Escherichia coli in tenderized (non-intact) beef. 2.2. Determine cook dwell times for ground meat products, with and without marinade or other enhancing solutions, using common consumer preparation methods such as cooking on gas or electric grills at internal instantaneous temperatures ranging from 120' to 160°F. 3. Develop and/or validate strategies to deliver antimicrobials to raw and packaged foods from production through to consumption. 3.1. Derive data to aid verification of growth inhibitor effectiveness for L. monocytogenes in RTE products from time of production through consumption.
1b. Approach (from AD-416)
Identify where pathogens enter the food supply, how they persist, and/or what can be done to eliminate or control them. The target pathogens of greatest concern for this proposal are Listeria monocytogenes and Shiga toxin-producing Escherichia coli, but other pathogens may also be evaluated. The targeted foods are raw and ready-to-eat (RTE) meat, poultry, and dairy products, as well as raw and further processed non-intact meats. Identify sources of L. monocytogenes in foods or food processing and retail environments and to elucidate factors contributing to its survival and persistence. Molecular methods such as pulsed-field gel electrophoresis (PFGE) and multilocus genotyping (MLGT) will be used to differentiate isolates from various sources from the farm through distribution and at retail to determine pathogen niche and succession. Validate processes and interventions such as fermentation, high pressure processing, food grade chemicals, and heat (cooking), alone or in combination, to inhibit/remove undesirable bacteria and better manage pathogen presence, populations, and/or survival during manufacture and storage of target foods. The proposed research to find, characterize, and kill pathogens along the food chain continuum will expand our knowledge of important food borne pathogens and lead to better methods for controlling them in foods prior to human contact and consumption, thereby enhancing the safety of our Nation’s food supply.
3. Progress Report
The overarching goals are to identify where pathogens enter the food supply, how they persist, and/or what can be done to eliminate or control them. The target pathogens are Listeria monocytogenes (Lm) and Shiga toxin-producing Escherichia coli (STEC), and the targeted foods are raw and ready-to-eat (RTE) meat, poultry, and dairy products, as well as raw and further processed non-intact meats. Regarding the former pathogen, in collaboration with the DHHS, Food and Drug Administration (FDA) and the USDA, Food Safety and Inspection Service (FSIS) we have collected several thousand ready-to-eat (RTE) foods from retail establishments in four FoodNet sites (California, Maryland, Connecticut and Georgia) and implemented screening and enumeration methods to test these foods for Lm and to subtype the isolates recovered. These efforts will continue for a 12-month period to quantify the prevalence and levels of Lm in target RTE foods at retail and to elucidate factors contributing to its survival and persistence. In related studies, we monitored the fate of Lm on the surface of specialty/ethnic meats, namely scrapple and goetta, and evaluated several food grade antimicrobials as antilisterial ingredients in the former. Results to date confirm that both products provide a favorable environment for growth of Lm and that antimicrobial blends are effective at controlling outgrowth of this pathogen during refrigerated shelf life. With regards to STEC, in collaboration with industry and academic partners we have identified and evaluated several food grade chemicals and surface-treated inoculated beef subprimals prior to mechanical or chemical enhancement and cooking of the non-intact beef. Studies are ongoing to optimize the combination, concentrations, and volumes of these antimicrobials for control of STEC associated with non-intact beef. We also determined the thermal death times of individual strains of STEC used in studies to tenderize and cook inoculated beef subprimals.