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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

2020 Annual Report

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.

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.

Progress Report
This project will end January 18, 2021. New NP108 OSQR is entitled “Incidence of bacterial pathogens in regulated foods and applied processing technologies for their destruction” and is under revision. We addressed all milestones for Project 8072-41420-019-00D via productive collaborations with CRADA/MTRA partners and food safety professionals from academia, government, industry, and consumer groups. Programmatically, we quantified the prevalence, levels, and types of target pathogens along the food chain continuum from farm to flush and developed and validated biological, chemical, and physical interventions to control Listeria monocytogenes (Lm), Shiga toxin-producing Escherichia coli (STEC), Salmonella spp. (Sal), Trichinella spiralis (Ts), and Toxoplasma gondii (Tg) in a variety of foods. Regarding pathogen presence, we established the comparative recovery rate of STEC in raw, non-intact veal and beef purchased at food retailers in the Mid-Atlantic states in the US: in general, STEC were recovered more frequently from raw veal than beef, and non-O157 STEC were more common than serotype O157:H7 cells. In related experiments, the inability to recover viable cells of STEC displaying serogroup-specific surface antigens for at least one of the seven regulated serogroups of STEC in combination with the stx and eae virulence genes suggests that STEC are not common in raw ground pork or in marinades (fresh and spent) from specialty grocers or food retailers in the Mid-Atlantic states in the U.S. We also quantified the prevalence of Sal in raw chicken livers from food retailers, research farms, and abattoirs. Whereas the pathogen was recovered quite often from raw chicken livers purchased at food retailers (ca. 60%; 6.4 MPN to 2.4 log CFU/g), Sal was recovered less frequently from livers harvested from birds on a research farm (ca. 5.8%; 0.4 to 2.2 MPN/g) or from livers obtained at a poultry slaughter facility (6.7%). Studies are ongoing to subtype the isolates retained from the abovementioned surveys. As part of a large-scale market basket survey, we used whole genome sequencing (WGS) to characterize 201 isolates of Lm recovered from 102 of 27,389 (RTE) foods purchased at grocery stores in the U.S. over a two-year period. Although significant differences in genetic diversity were not found following pairwise comparisons of isolates, differences in virulence potential and possible sources of the pathogen were observed. Collectively, these data provide insight on the true prevalence, levels, and types of pathogens in higher volume and/or higher risk foods, as well as their relatedness, persistence, and source(s) and this, in turn, should lead to better management of pathogens in foods and lower public health risks. Regarding pathogen control and interventions, we monitored the viability or improved the safety and/or extended the shelf life of raw, further processed, and/or fermented foods by applying high pressure or heat or by treating such products with food grade chemicals as surface agents or ingredients. Antimicrobials were effectively and efficiently delivered into foods as ingredients or onto foods via SLIC® or electrostatic spraying. Examples include the use of organic acids and/or buffered vinegar, a “clean label” food grade chemical, to control Lm in rotisserie chicken salad, uncured turkey breast, mortadella, or ham, as well as monitoring the fate of STEC, Lm, and/or Sal on slices of prosciutto and pancetta. We also tested if dry/fermented sausage or dry-cured hams provided a favorable environment for persistence or outgrowth of Ts or Tg during manufacture or during extended (up to 12 months) shelf life. For specialty/ethnic products we assessed viability of STEC in “soupie”, a home-made soppressata, as well as in soppressata that we prepared with certified angus beef, and both sliced retail and bresaola we prepared, to validate safe processes for these specialty/ethnic products. We also validated post-fermentative heating temperatures and times to control pathogens in several types of dry/fermented sausage, including pepperoni- and Genoa-type sausage. We also demonstrated that well-established cooking and pressure parameters required to eliminate STEC, Sal, and Lm from ground beef should be as effective for controlling cells of these same pathogens in a plant-sourced meat. We also analyzed the effect of experimental parameters such as cooking appliance, volume and type of cooking oil, product formulation, levels and types of antimicrobials, and cooking/fermentation times and temperatures on thermal inactivation of target pathogens in red meat and poultry products. As expected, the higher the temperature and the longer the time for application of heat or fermentation/drying, the greater the reduction in pathogen levels. Lastly, in collaborator with several of our academic partners we developed a message for the masses media/marketing campaign (aka “160° is Good”) to inform consumers about proper thermometer use and that burgers should be cooked to 160°F. Social media was also used to better educate consumers about real versus perceived food safety risks in a retail setting. These data have real world application for maintaining the safety of our Nation’s food supply via our frequent input from regulators and the food industry and our use of pathogenic strains and pilot-scale processing equipment.

1. Eliminating pathogens within plant burgers using heat and high pressure. Interest in plant-based burgers has grown appreciably in recent years. While some information is available on the sensory and quality attributes, little is known as to the safety of such products. Research by ARS scientists at Wyndmoor, Pennsylvania, showed that cooking burgers in a saute pan or treating burgers with high pressure significantly lowered levels of Listeria monocytogenes and toxigenic Escherichia coli. In fact, both pathogens responded similarly to heat and high pressure in plant-and beef-based burgers. These findings confirmed that well-established cooking and pressurization treatments for ground beef are equally effective for ensuring the safety of burgers made from a plant-sourced protein.

2. Characterization of Listeria monocytogenes recovered from ready-to-eat (RTE) foods. Listeria monocytogenes (Lm) is a common and deadly pathogen that is found on a variety of RTE foods. Additional data are needed to determine the source and relatedness of Lm associated with high-volume, higher-risk RTE foods from grocery stores. Between 2010 and 2013, ARS researchers at Wyndmoor, Pennsylvania, in collaboration with Food and Drug Administration (FDA) researchers at College Park, Maryland, conducted DNA fingerprinting on 201 isolates of Lm recovered from 102 of 27,389 foods purchased at representative grocery stores in the U.S. The results established the relatedness of all isolates and provided unique insights on the sources of this pathogen between and among foods and stores. These findings will lead to better strategies to lower the risk of listeriosis prior to human contact or consumption with Lm.

3. Inactivation of parasites in dry-cured ham. Consumption of raw and uncooked pork meat has been associated with transmission of toxoplasmosis, a serious illness caused by Toxoplasma gondii. Because of the sporadic presence of T. gondii in pork meat, consumption of some pork products may present a potential risk for transmission of toxoplasmosis. In collaboration with ARS researchers at Beltsville, Maryland, ARS researchers at Wyndmoor, Pennsylvania, monitored viability of T. gondii in experimentally-infected, dry-cured whole hams processed using standard methods. T. gondii was inactivated during the early stages of ham manufacture and was not detected during periodic sampling over the 12-month duration of this experiment. Thus, approved protocols for production of dry-cured hams validated can lower the risk of toxoplasmosis to consumers and help industry/processors meet existing regulatory requirements.

4. Application of heat to control pathogens in Genoa salami. Pathogens such as Salmonella can be recovered from Genoa salami, and consumption of fermented meats harboring such pathogens has sporadically caused human illness. Traditional processes for preparing Genoa salami may not be effective to inactivate pathogens to the extent necessary to meet statutory requirements, and without affecting product quality. Thus, ARS researchers at Wyndmoor, Pennsylvania, evaluated the effect of post-fermentation heating times and temperatures in combination with drying on the fate of Salmonella in Genoa salami. Researchers heated salami just after fermentation, which combined with the typical drying regimen for Genoa, lowered levels of Salmonella. These data provide the industry with time/temperature options to kill Salmonella in Genoa salami and to meet regulatory requirements without appreciably compromising product quality.

5. High-pressure processing of meatballs to control pathogens. Consumption of under-processed and improperly handled or stored meat products contaminated with Escherichia coli (E. coli) that produce Shiga toxins are responsible for numerous illnesses, hospitalizations, and deaths each year. Over the past 20 years, multiple recalls and illnesses were linked to raw ground beef, and recent recalls were also linked to meatballs. ARS scientists at Wyndmoor, Pennsylvania, used high-pressure processing to inactivate toxigenic E. coli in raw meatballs. Using high-pressure treatment to kill pathogen in raw meatballs will lower the public health risk from toxigenic E. coli.

Review Publications
Jackson-Davis, A., Daniel, M., Luchansky, J.B., Porto Fett, A.C., Kassama, L. 2019. The efficacy of ultrasound on the inactivation of Shiga toxin-producing Escherichia coli in raw beef trim. Foods. 2(5).
Jung, Y.N., Porto Fett, A.C., Shoyer, B.A., Shane, L.E., Henry, E.D., Osoria, M., Luchansky, J.B. 2019. Survey of intact and non-intact raw pork collected at retail stores in the mid-Atlantic region of the United States for the seven regulated serogroups of Shiga toxin-producing Escherichia coli. Journal of Food Protection. 82.
Luchansky, J.B., Shoyer, B.A., Jung, Y.N., Shane, L.E., Osoria, M., Porto Fett, A.C. 2020. Viability of Shiga Toxin-producing Escherichia coli, Salmonella, and Listeria monocytogenes within plant burgers and beef burgers during cold storage and following pan frying. Journal of Food Protection. 83(3):434-442.
Porto Fett, A.C., Shane, L.E., Shoyer, B.A., Osoria, M., Jung, Y.N., Luchansky, J.B. 2020. Viability of cells of shiga-toxin producing Escherichia coli and Listeria monocytogenes within plant-sourced versus beef-sourced protein samples in response to high pressure. Journal of Food Protection.
Porto Fett, A.C., Jackson-Davis, A., Kassama, L., Daniel, M., Oliver, M., Jung, Y.N., Luchansky, J.B. 2020. Inactivation of Shiga toxin-producing cells of Escherichia coli in refrigerated and frozen meatballs using high pressure processing. Microorganisms.
Chen, Y., Chen, Y., Pouillot, R., Dennis, S., Xian, Z., Luchansky, J.B., Porto Fett, A.C., Lindsay, J.A., Allard, M., Brown, E., Van Doren, J.M. 2020. Genetic diversity and virulence gene profiles of Listeria monocytogenes isolates from the 2010-2013 interagency market basket survey. PLoS One.