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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Characterization and Interventions for Foodborne Pathogens » Research » Research Project #439564

Research Project: Incidence of Bacterial Pathogens in Regulated Foods and Applied Processing Technologies for Their Destruction

Location: Characterization and Interventions for Foodborne Pathogens

2022 Annual Report

Objective 1: Determine the recovery rate, population levels, relatedness, persistence, and harborage sites of target pathogens in raw, further processed, and/or ready-to-eat foods from production through to consumption to assist in risk assessments and communication. [C1, PS1] Sub-Objective 1.A: Determine the prevalence and levels of Lm, STEC, and Salmonella in RTE foods at retail, raw organ meats from abattoirs, and frozen bakery products containing meat and vegetables from food retailers. Sub-Objective 1.B: Determine the relatedness of Lm, STEC, and Salmonella recovered from foods using molecular typing methods such as PFGE and WGS. Sub-Objective 1.C: Assess perceptions, food safety attitudes, and self-reported behaviors related to observed food safety hazards by consumers who shop at grocery stores. Objective 2: Validate lethality (heating) and stabilization (cooling) processes for ready-to-eat (RTE) and not ready-to-eat (NRTE) meat and poultry products. [C1, PS5] Sub-objective 2.A: Validate lethality and stabilization processes to control of Salmonella, Lm, and Cperf in non-intact and specialty/ethnic pork and beef products. Sub-objective 2.B: Validate consumer-relevant cooking times, temperatures, and appliances to control target pathogens in (multi-species) bakery products containing meat and vegetables. Sub-objective 2.C: Validation of cooking and cooling profiles for large mass meat products to achieve stabilization performance standards that prevent growth of Cperf. Objective 3: Develop, optimize, and validate biological, physical, and chemical interventions and processes to control target pathogens in raw, RTE, and specialty/ethnic foods. [C1, PS5] Sub-objective 3.A: Apply interventions to control target pathogens in RTE meats and multi-component meat-based salads and salsas. Sub-objective 3.B: Validate food-relevant interventions to control target pathogens in plant-sourced meat alternatives. Sub-objective 3.C: Evaluation of the impact of processing parameters of dry-cured fermented meat on lethality towards STEC, Salmonella, and Lm. Sub-objective 3.D: Develop and/or validate strategies to control pathogens in forcemeats.

The overarching theme of this research plan is to identify where pathogens enter the food supply, where, how, and why they persist in foods, and/or what can be done to reduce their levels or to eliminate them along the farm to fork continuum. Target pathogens will include Listeria monocytogenes (Lm), Salmonella, Clostridium perfringens (Cperf), and Shiga toxin-producing cells of Escherichia coli (STEC). Target foods will include raw and ready-to-eat meats, dairy, baked foods, and vegetables, as well as simulated meats and specialty/ethnic foods, targeted for human and animal consumption. A primary focus will be to identify entry points, sources, and levels of target pathogens in foods or within food processing, food service, and retail environments, and to elucidate factors contributing to their survival and persistence. Phenotypic and molecular methods, including pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS), will be used to identify and differentiate isolates from the farm through distribution and at retail to determine pathogen relatedness, niche, persistence, and succession. Another focus will be to validate processes and interventions such as fermentation, drying, high pressure, biopreservatives, food grade chemicals, and heat (e.g., grilling and sous vide), alone or in combination, to inhibit/remove undesirable bacteria and better manage pathogen presence, populations, and/or survival during manufacture and/or subsequent storage of target foods. We will also develop and optimize methods to deliver antimicrobials to food systems, including electrostatic spraying and various strategies to introduce interventions into/onto foods or food containers/packaging (e.g., SLIC®). Our findings will assist numerous producers and processors with meeting current regulatory guidelines and assist regulators such as the DHHS FDA and the USDA FSIS with making science-based policy decisions, thereby enhancing the safety of the Nation’s food supply.

Progress Report
In association with our CRADA partner and with key players from within academia, government, industry, and consumers sectors, in Fiscal Year (FY) 2022 we made measurable progress on our approved milestones and deliverables. In brief, our research is directed toward the recovery, characterization, and control of target pathogens at various points along the continuum from food production through to consumption. To this end, we continued to develop and validate biological, chemical, and physical interventions to control Listeria monocytogenes (Lm), Shiga toxin-producing Escherichia coli (STEC), and Salmonella species (Sal) in a variety of foods. Examples include, quantifying inactivation of Lm and STEC in specialty/niche meats such as a homemade soppressata (aka “soupie”) and on slices of commercial bresaola, a dry-cured, whole-muscle, ready-to-eat (RTE) beef product. Other examples include evaluation of organic acids and their salts along with other clean label alternatives to control Lm on olive loaf and bologna, both of which are higher-volume and potentially higher-risk RTE delicatessen-type meats. For some of these inoculated product studies, the food grade antimicrobials were delivered into foods as ingredients, whereas in other studies the antimicrobials were delivered onto foods using the Sprayed Lethality in Container (SLIC) method or the technology of air assisted electrostatic spraying (ESS). These delivery strategies are, in general, more efficient and cost effective than traditional options for introducing antimicrobials into food systems. In collaboration with our sister agency, the USDA Food Safety and Inspection Service, using funding provided by an Interagency Agreement, we recently initiated studies to monitor the effect of water activity, time, and temperature on viability of Lm and Sal inoculated into country hams or into bakery products containing meat (i.e., meat/pot pies). These ongoing studies address potential data gaps in the recently revised USDA FSIS Guidelines for cooking (i.e., Appendix A) and cooling (i.e., Appendix B) of red meat and poultry products. We also expanded our studies to evaluate post-fermentation heating of Genoa salami to control Sal. In addition to heating times/temperatures (46.3 versus 48.9 degrees C), we also evaluated endpoint fermentation pH (pH 5.1 versus pH 4.7) and casing size (54 mm versus 105 mm). The results confirmed that pathogen levels were lowered by at least 100,000 cells per gram and that higher heating temperatures and longer heating times, along with low endpoint pH, provided greater reductions in levels of Sal. These data are significant since it allows for a safer product while at the same time reducing processing time. Collectively, the experiments and associated results addressed above are of practical relevance as food safety professionals from industry and government were fully engaged from the outset and because we used pathogenic strains and pilot scale food processing equipment in our specially-constructed pathogen compatible food processing suite. The resulting ground-truth data are ready for immediate implementation and have significant potential to enhance product safety/quality and reduce the overall public health risk.

1. Confirmation that Listeria monocytogenes (Lm) and Shiga toxin-producing Escherichia coli (STEC) do not grow on sliced bresaola. Bresaola is one example of a specialty-type meat that has experienced an increase in popularity in the United States due to its inclusion on charcuterie boards. As a dry-cured, whole-muscle ready-to-eat (RTE) meat product, the quality and safety attributes of bresaola rely solely on a decrease in water activity (aw) during its salting/curing and drying/maturation steps. Given the potential for process deviations or post-process contamination, ARS researchers at Wyndmoor, Pennsylvania, monitored viability of Lm and STEC inoculated onto commercial slices of bresaola. The results confirmed that pathogen levels decreased by 250 to 1000 cells per gram after six months of refrigerated storage. Thus, bresaola does not support outgrowth of Lm or STEC and can be included and safely consumed on charcuterie trays.

2. Inactivation of Listeria monocytogenes (Lm) and Shiga toxin-producing Escherichia coli (STEC) in a homemade Soppressata. Fermented sausage such as soppressata can on occasion harbor pathogens such as Lm and STEC. From a public health perspective, there may be greater concern for pathogen presence and persistence for artisanal products made in the home due to the increased handling and lack of adequate or consistent monitoring and control of key parameters during processing such as time, temperature, pH, and moisture levels. Thus, ARS researchers at Wyndmoor, Pennsylvania, evaluated the effect of fermentation and storage on the fate of Lm and STEC in a homemade soppressata or “soupie”. Fermentation and drying lowered pathogen levels by about 100 cells per gram of soupie, whereas further storage at room temperature for about 1-4 months lowered pathogen levels by at least 100,000 cells per gram. These data confirm that homemade soppressata does not support pathogen survival and it provides consumers with a protocol that yields a safe product without compromising quality.

3. Validation of a food gade antimicrobial blend to control pathogens in a ready-to-eat (RTE) ethnic meat. Post-processing surface contamination of RTE meats with foodborne pathogens is a significant public health concern to regulatory agencies and the food industry because such products may support pathogen persistence or may be consumed without additional cooking. Thus, ARS researchers at Wyndmoor, Pennsylvania, validated the efficacy of a blend of organic acids to control outgrowth of L. monocytogenes (Lm) and Salmonella spp. (Sal) on a German-style bologna during extended shelf life. The bologna was formulated with a blend of the salts of two organic acids (0.9 to 2.6%), sliced, inoculated with a multi-strain cocktail of cells of Lm or Sal to a target level of ca. 6,000 cells per gram, and then stored at 4degC for up to 90 days. Inclusion of these antimicrobials as ingredients in bologna was effective at precluding outgrowth of Lm or Sal throughout shelf life. These data will allow meat processors to enhance the safety of their product/process as well as to satiate existing regulatory requirements.

Review Publications
Luchansky, J.B., Shoyer, B.A., Shane, L.E., Osoria, M., Campano, S.G., Porto Fett, A.C. 2022. Inactivation of Listeria monocytogenes and Shiga toxin-producing Escherichia coli in "soupie", a homemade soppressata. Food Protection Trends. 42(1):48–57.
Porto Fett, A.C., Espuna, E., Shane, L.E., Shoyer, B.A., Mcgeary, L., Stahler, L., Osoria, M., Luchansky, J.B. 2022. Viability of Shiga toxin-producing Escherichia coli, Salmonella spp., and Listeria monocytogenes during preparation and storage of Fuet, a traditional dry-cured Spanish pork sausage. Journal of Food Protection.