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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Food Safety and Intervention Technologies Research » Research » Research Project #429829

Research Project: Bacterial Pathogens in Regulated Foods and Processing Technologies for Their Elimination

Location: Food Safety and Intervention Technologies Research

2017 Annual Report


1a. Objectives (from AD-416):
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 and levels of L. monoctyogenes, STEC, and Salmonella spp. in RTE foods at retail, as well as at abattoirs/processing plants. 1.2. Determine the relatedness of L. monoctyogenes, STEC, and Salmonella spp. recovered from foods using molecular typing methods such as PFGE and MLGT. 1.3. Assess perceptions, food safety attitudes, and self-reported behaviors related to observed food safety hazards by consumers who shop at grocery stores. 2: Develop, optimize, and validate processing technologies for eliminating pathogens. 2.1 - Determine the transfer and survival of STEC and Salmonella spp. in ground and tenderized (i.e., non-intact) red meat, pork, pet, and poultry products. 2.2 - Determine cook dwell times for ground poultry products using common consumer preparation methods such as cooking on gas or electric grills at internal instantaneous temperatures ranging from 100° to 160°F for lethality towards Salmonella and STEC and for consumer acceptability. 2.3 - Determine the effectiveness of food grade antimicrobials applied via electrostatic spray and Sprayed Lethality in Container (SLIC®) methods on pork offal and on chicken necks and frames for control of Salmonella and STEC. 2.4 - Validate fermentation and cooking of dry-fermented sausages for control of STEC, Salmonella, and other pathogens. 3: Develop and/or validate strategies to deliver antimicrobials to raw and packaged foods from production through to consumption to control L. monocytogenes, STEC, Salmonella spp., and other pathogens.


1b. Approach (from AD-416):
We will exploit the tools of microbiology, molecular biology, and food science to recover, characterize, and control food borne pathogens from production through to consumption for a variety of foods, with emphasis on specialty/ethnic and higher volume, higher risk foods. We will identify where pathogens enter the food supply, determine how they persist, and investigate biological, chemical, and physical interventions to eliminate or better manage them to improve public health. The target pathogens of greatest concern for this project are Listeria monocytogenes, Salmonella spp., Shiga toxin-producing Escherichia coli, Trichinella spiralis, and Toxoplasma gondii. Targeted foods would include, but not be limited to, raw and ready-to-eat (RTE) meat, poultry, pet, and dairy foods, as well as raw and further processed non-intact meats. One focus of the proposed research is to identify sources and niches of the above mentioned pathogens in foods and food processing environments, as well as at retail and food service establishments, to gain insight on factors contributing to their survival and persistence. Multiple isolates recovered from each sample testing positive from such surveys will be retained for further characterization by phenotypic and genotypic (e.g., pulsed-field gel electrophoresis, PCR-based methods, and/or whole genome sequencing) methods to establish relatedness of isolates and their source and succession. As another focus of our research, efforts will be made to validate processes and interventions such as fermentation, high pressure processing, food grade chemicals, and heat, alone or in combination, to inhibit/remove undesirable bacteria from the food supply and to better manage their presence, populations, and/or survival during manufacture and storage of target foods/feed. The proposed research to find, characterize, and kill pathogens along the food chain continuum will expand our knowledge of the most prevalence/potent food borne pathogens and help us to elaborate better methods for controlling them in foods prior to human contact or consumption, thereby enhancing the safety of our global food supply.


3. Progress Report:
Progress was made on all objectives, all of which fall under NP108 –Food Safety, Component 1 Foodborne Contaminants; Problem Statement 5. Intervention and Control Strategies, Including Mycotoxins. We continue to benefit from and nurture our longstanding and impactive collaborations with research partners from academia, government, industry, and consumer groups in the conduct of our research to recover, characterize, and control target bacterial and parasitic pathogens in both higher volume/risk and specialty/ethnic foods. Our collaborators include various CRADA, RSA, and MTRA partners, as well as producers, processors, regulators, technology providers, consumer groups, and academicians with the shared interest in enhancing the safety of our Nation’s food supply. Our collective efforts have resulted in numerous tangible outcomes. Examples of our current research includes studies to develop and validate biological, chemical, and physical interventions to control Listeria monocytogenes (Lm), Shiga toxin-producing Escherichia coli (STEC), Salmonella spp. (Sal), Trichinella spiralis (TS), and/or Toxoplasma gondii (TG) in or on a variety of raw, fermented, cooked, and further processed foods, including non-intact products, as well as ready-to-eat (RTE) foods. One example is a process validation study on the inclusion of food grade chemicals in/on frankfurters to control Lm during extended refrigerated/frozen storage. Another example of a process validation study is the use of buffered vinegar, a “clean label” food grade chemical, to reduce levels and/or prevent outgrowth of Lm during storage of mortadella, a Italian-style RTE delicatessen meat. In addition to optimizing the levels and placement of antimicrobials into/onto target foods, we continue to exploit the Sprayed Lethality in Container (SLIC) and air assisted electrostatic spray (ESS) technologies to deliver antimicrobials to foods, such as beef subprimals and raw chicken breasts, at lower costs along with lower volumes and superior coverage compared with more traditional antimicrobial dips and sprays. Considerable efforts and resources were also directed to establish time and temperature parameters to maximize thermal inactivation of STEC and Sal in raw and further processed red meat and poultry products, including non-intact products, such as dry-fermented sausage, ground poultry, subprimals, and meat bars. The combined effects of lowering of pH, increasing time and temperature of cooking, and decreasing water activity were further elaborated in these latter studies. As expected, the higher the temperature and the longer the time for application of heat, the greater the reduction in pathogen levels. In related studies, in collaboration with ARS scientists, we quantified viability of TG and TS in a pepperoni-type fermented sausage made form pork harvested from swine that were inoculated with the above mentioned parasites. As a final example of our progress, we conducted large scale and multi-institutional surveys of higher-volume, higher-risk retail foods, notably cig kofte from Ankara, Turkey, and raw veal from the mid-Atlantic region of the United States, to determine the recovery rate, levels, and harborage points for Lm, Sal, and STEC. Multiple isolates retained from each sample testing positive for a target pathogen were subtyped and characterized for pathogenic potential and survival attributes. Lastly, it should be noted that our process validation studies facilitate taking our findings to real-world abattoirs and processing plants in support of food safety programs because we use pathogenic strains and pilot-scale processing equipment, we inoculate and process real/entire foods rather than simulated or re-structured products, and we seek industry guidance and regulator participation throughout the planning, conduct, and dissemination phases. Thus, our research has immediate practical use and direct implementation by the industry and a focused and positive impact on public health in general.


4. Accomplishments
1. Food safety at grocery stores. Retail grocery store shoppers and employees view food safety risks differently than food safety experts and as a result may be at higher risk for becoming sick. In collaboration with scientists at North Carolina State University, ARS researchers at Wyndmoor, Pennsylvania, collected about 120 digital photographs at grocery stores in California, Maryland, Connecticut, and Georgia of both possible and actual food safety risk situations. As examples, photographs captured utensils, such as tongs, placed handle-down in containers of uncovered foods that are ready-to-eat, bare-handed contact of deli meat during slicing, and water dripping from the ceiling onto the deli counter. These digital photographs can be used as a motivation and as a real-world teaching tool to better inform shoppers and employees at grocery stores of good practices.

2. Control of Shiga toxin-producing Escherichia coli (STEC) surrogates on veal carcasses. Results collected by the USDA suggest there are more Shiga toxin-producing Escherichia coli (STEC) on veal products than on beef products. As part of a multi-institutional team that included Kansas State University, University of Nebraska-Lincoln, and Texas A&M University, ARS researchers at Wyndmoor, Pennsylvania, tested lactic acid (4.5%, pH 2.0), a blend of hydrochloric and citric acids (pH 1.2), and a blend of lactic and citric acids (2.25%, pH 2.3) on veal carcasses to eliminate a combination of E. coli strains that are similar to STEC except not pathogenic. A standard water wash (about 50degC) reduced the E. coli population by 8 cells per cm square on the veal carcasses. All three antimicrobial sprays applied to pre-rigor carcasses delivered an additional reduction of 5 cells of E. coli per cm square, whereas chilling of carcasses for 24 h reduced the surrogate population by only an additional 3 cells per cm square. This study demonstrated that warm water washing, followed by a pre-chill spray treatment with the chemicals tested in this study, can improve the safety of veal carcasses.

3. Control of Listeria monocytogenes (Lm) on clean label/natural ready-to-eat (RTE) meats. Not much information has been published on the effectiveness of natural antimicrobials to eliminate pathogens on specialty/ethnic RTE meats. In collaboration with our CRADA partners, ARS researchers at Wyndmoor, Pennsylvania, conducted research to determine if buffered vinegar (BV) or a blend of potassium lactate and sodium diacetate (KLac) were effective to control Lm on freshly-manufactured mortadella. This bologna-like product was formulated with or without 1.0 or 1.5% of liquid BV (LBV), 0.6 or 1.0% of dry BV (DBV), or 2.5% of KLac, inoculated with ca. 6,500 cells of Lm per slice, and then stored refrigerated. In the absence of antimicrobials, Lm numbers increased by ca. 200 cells/slice after 120 days at 4 deg C. With inclusion of LBV, DBV, or KLac as ingredients, pathogen numbers decreased by ca. 2 to 10 cells per slice after 120 days at 4 deg C. Inclusion of 1% LBV or DBV, as clean label ingredients, in mortadella is equally effective as 2.5% KLac (10 cells reduction) to control Lm on mortadella during proper refrigerated storage.

4. Ensuring the safety of fuet, a Spanish-style fermented sausage. Foodborne pathogens such as Salmonella spp. (Sal), Shiga toxin-producing Escherichia coli (STEC), and Listeria monocytogenes (Lm) may survive in some fermented meats. In collaboration with our CRADA partners, ARS researchers at Wyndmoor, Pennsylvania, conducted research on the survivability of cells of Sal, Lm, and STEC in fuet. Ground pork (30% fat) was mixed with salt (2.5%), starter culture, and spices, and then inoculated with a pool of cells (ca. 6 million cells) of either STEC, Sal, or Lm. This inoculated meat batter was stuffed into casings, fermented at 23 +/- 2 deg C and ca. 95 +/- 4% relative humidity (RH) to ca. pH 5.3, and then dried (12 +/- 2 deg C and ca. 75-85% RH to a water activity of 0.86 or 0.89). The results showed total reductions of greater than 12,500 to 200,000 cells per gram of all three pathogens were achieved after drying. These data will assist manufacturers with ensuring that fuet is wholesome.

5. Inactivation of Trichinella spiralis in dry-cured pork sausage. Although trichinosis from ingestion of raw or uncooked pork remains a problem worldwide, little information is available on how to inactivate Trichinella in fermented products. In collaboration with ARS researchers at Beltsville, Maryland, ARS researchers at Wyndmoor, Pennsylvania, evaluated the anti-trichinae effect of salt, moisture, pH, and temperature during fermentation and drying of a dried-cured pork sausage. Results demonstrated that salt concentrations above 1.3%, in combination with fermentation to pH 5.2 or below, inactivated greater than 96% of Trichinella larvae within 24 to 28 h. After 7 to 10 days of drying, Trichinella were inactivated. The process for making pork sausage as tested in this study was effective for killing Trichinella spiralis, and can be used by meat processors to make sure their products are safe.


Review Publications
Luchansky, J.B., Chen, Y., Porto Fett, A.C., Pouillot, R., Shoyer, B.A., Johnson-Derycke, R., Eblen, D.R., Shaw, W.K., Van Doren, J.M., Catlin, M., Lee, J., Tikekar, R., Gallagher, D., Lindsay, J.A., Adams, A., Agnella, S., Akingbade, D., Ayala, A., Baker, E.G., Barlow, K., Bauer, N., Benjamin, L.A., Berry, K., Call, J.E., Campano, S.G., Cook, V., Gallagher, D., Gathercole, L., Ghazzi, D., Govoni, J.A., Hay, G., Harvey, C., Hoelzer, K., Kanjanakorn, A., Kause, J., Khokhar, S., King, J., Klein, V., Lopez, J., Martino, K., Mbandi, E., Murphy, M., Nasella, J., Nguyen, T., Oryang, D., Osoria, M., Papadakis, L., Rajakumar, A., Reed, C., Same, M., Shane, L., Spurlino, C.A., Starks, H.E., Torrence, M.E., Williams, L., Wadsworth, S., Wyszkowski, K., Yoo, K., Dennis, S. 2017. Survey for Listeria monocytogenes on ready-to-eat foods from retail establishments in the United States (2010-2013): assessing potential changes of pathogen prevalence and levels in a decade. Journal of Food Protection. 80:903-921.