Listeria Monocytogenes in Ready-to-eat Meat Products: Risks, Controls and Education for Prevention

It is estimated that Listeria monocytogenes causes 2,493 cases of listeriosis and 499 deaths annually in the United States; most of the cases involve elderly, pregnant women and their fetuses, and immunocompromised individuals. Two major recent initiatives, specifically, the interim final rule for control of L. monocytogenes and the L. monocytogenes risk assessment for ready-to-eat foods were undertaken by the United States Department of Agriculture Food Safety and Inspection Service (USDA-FSIS) and the United States Food and Drug Administration (FDA) to meet two general objectives: to assess the magnitude of risk from consumption of contaminated ready-to-eat (RTE) foods; and to establish requirements for the industry to apply procedures for better control of L. monocytogenes in RTE meat and poultry products. The risk assessment effort identified data gaps relative to L. monocytogenes in RTE foods, which need to be filled before the risk assessment is updated. Therefore, research studies are needed to fill these data gaps, as well as for the identification of treatments, formulations and processes to be recommended for use by the industry in its efforts to meet the requirements of the recent final rule in order to control the pathogen. Furthermore, studies need to be conducted to identify potential risks associated with common household food handling practices by consumers and to propose precautions or measures that may allow further enhancement of the safety of foods for sensitive individuals, even beyond the level of safety provided by industry efforts. The new knowledge needs to be transmitted to regulators, risk assessors, the industry, consumers, health care providers and food service managers, in order to improve the safety of RTE meat and poultry products. Thus, the objectives of this project are to: (i) evaluate survival and growth kinetics (i.e., death or growth rates) of L. monocytogenes under various time-temperature conditions of storage of commercial RTE meat and poultry products selected on the basis of the relative risk ranking developed by the FDA and the USDA-FSIS risk assessment; (ii) investigate alternative antimicrobial treatments, formulations or processes for higher risk products that may be used by the industry to select alternatives for L. monocytogenes control as required by the new regulations; (iii) use the data obtained to develop predictive mathematical models for L. monocytogenes survival or growth in various products under various conditions of processing, handling and storage; (iv) evaluate consumer practices that may lead to cross-contamination in the home and develop potential interventions to reduce or inactivate potential L. monocytogenes contamination on higher risk RTE products or those for which control is difficult; (v) develop research-based educational materials and training modules designed to promote adoption of food selection, preparation, handling and storage practices that decrease the risk of foodborne listeriosis; and, (vi) conduct extension education activities to disseminate such findings to at-risk groups, their health care providers and dietary managers of elderly feeding institutions.

A major concern for the meat processing industry, regulators and consumers is the potential for contamination of ready-to-eat meat and poultry products with the pathogen Listeria monocytogenes after the products have undergone a pathogen lethality process; such contamination may occur during product slicing and/or packaging. This project will evaluate potential human health risks and develop procedures for control of the pathogen at the production and consumption level.

Exploratory studies will be conducted in broth and model product formulations to aid in screening of antimicrobial agents, treatments and processes, and in selection of parameters that may potentially enhance the safety of ready-to-eat (RTE) meat and poultry products through inactivation or control of Listeria monocytogenes. Further investigation to meet the specified objectives will be conducted using commercial RTE meat and poultry products, as fresh after production as possible, from manufacturers or from local supermarkets. The procedures that will be applied will depend on the specific objective and will be based on previous methods used in our laboratory, published research, or approved methodologies, and where necessary and appropriate, new methodologies will be developed. Specifically, selection of RTE meat and poultry products will be based on the relative risk ranking developed by the United States Food and Drug Administration (FDA) and the United States Department of Agriculture Food Safety and Inspection Service (USDA-FSIS) to cover a representative range of meat and poultry products possessing different levels of risk (e.g., turkey breast, bologna, frankfurters). Inoculation of products will be accomplished using mixtures of L. monocytogenes strains isolated from foods, clinical samples or processing environments. Inoculated products will be vacuum packaged and stored at temperatures representing refrigeration (4C) and abuse (7C or 12C) conditions for periods of time based on label expiration dates or until the stationary phase of bacterial growth is reached. The survival and/or growth of the pathogen as well as total bacterial populations will be monitored during storage by plating on selective and general purpose media, respectively, as in previous studies. Indications of survival and estimations of growth potential will be used to calculate death or growth rates of the pathogen for each product and temperature combination through predictive mathematical modeling. Antimicrobial agents previously identified as effective against L. monocytogenes as well as novel antimicrobials will be evaluated in combination and/or in sequence for control of the pathogen. Additionally, commercial products with or without antimicrobials as ingredients in the formulation will be obtained from manufacturers or formulated in our laboratory to be either dipped or surface sprayed with antimicrobial solutions. Evaluation of consumer food-handling practices will be simulated using home refrigerator food contact surfaces such as plastic containers and packages. Inactivation treatments that will be investigated at the consumer level include heating or dipping in antimicrobial solutions readily available in the home (i.e., acetic and ascorbic acid), and the type of treatment will depend on the product tested. Audits will be conducted to determine unsafe food-handling practices at facilities serving meals to seniors, children and the immunocompromised, and to develop educational materials and safe food training modules for pregnant women, seniors, nurses and other health care professionals and dietitians and dietary managers of senior centers.

Two major recent initiatives, specifically, the interim final rule for control of Listeria monocytogenes and the L. monocytogenes risk assessment for ready-to-eat (RTE) foods, were undertaken by the United States Department of Agriculture Food Safety and Inspection Service (USDA-FSIS) and the United States Food and Drug Administration (FDA) to meet two general objectives: to assess the magnitude of risk from consumption of contaminated RTE foods; and to establish requirements for the industry to apply procedures for better control of L. monocytogenes in RTE meat and poultry products. The risk assessment effort identified data gaps relative to L. monocytogenes in RTE foods, which need to be filled before the risk assessment is updated. Therefore, research studies are needed to fill these data gaps, as well as for the identification of treatments, formulations and processes to be recommended for use by the industry in its efforts to meet the requirements of the recent final rule in order to control the pathogen. Furthermore, studies need to be conducted to identify potential risks associated with common household food handling practices by consumers and to propose precautions or measures that may allow further enhancement of the safety of foods for sensitive individuals, even beyond the level of safety provided by industry efforts. The new knowledge needs to be transmitted to regulators, risk assessors, the industry, consumers, health care providers, and food service managers, in order to improve the safety of RTE meat and poultry products. Thus, the objectives of this project are to: (i) evaluate survival and growth kinetics (i.e., death or growth rates) of L. monocytogenes under various time-temperature conditions of storage of commercial RTE meat and poultry products selected on the basis of the relative risk ranking developed by the FDA and the USDA-FSIS risk assessment; (ii) investigate alternative antimicrobial treatments, formulations or processes for higher risk products that may be used by the industry to select alternatives for L. monocytogenes control as required by the new regulations; (iii) use the data obtained to develop predictive mathematical models for L. monocytogenes survival or growth in various products under various conditions of processing, handling and storage; (iv) evaluate consumer practices that may lead to cross-contamination in the home and develop potential interventions to reduce or inactivate potential L. monocytogenes contamination on higher risk RTE products or those for which control is difficult; (v) develop research-based educational materials and training modules designed to promote adoption of food selection, preparation, handling and storage practices that decrease the risk of foodborne listeriosis; and, (vi) conduct extension education activities to disseminate such findings to at-risk groups, their health care providers and dietary managers of elderly feeding institutions. The procedures employed to achieve the objectives are based on previous methods used in our laboratory, published research, or approved methodologies, and where necessary and appropriate, new methodologies will be developed.

A major concern for the meat processing industry, regulators and consumers is the potential for contamination of ready-to-eat meat and poultry products with the pathogen Listeria monocytogenes after the products have undergone a pathogen lethality process such as heating. Such contamination may be introduced accidentally during product slicing and packaging. It is estimated that L. monocytogenes causes 2,493 cases of listeriosis and 499 deaths annually in the United States; most of the cases involve elderly, pregnant women and their fetuses, and immunocompromised individuals. This project will evaluate potential human health risks and develop procedures for control of the pathogen at the production, distribution and consumption level of ready-to-eat meat and poultry products, which have been associated with major listeriosis outbreaks in recent years. The results will be valuable to industry, health care providers and regulators in their efforts to reduce the incidence of listeriosis.