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United States Department of Agriculture

Agricultural Research Service

2010 Annual Report

1a.Objectives (from AD-416)
To evaluate, validate, and where necessary, develop new innovative, robust and valid predictive models for the responses of microbial pathogens, including foodborne threat agents, in select food matrices, as a function of: temperature, food formulation, competitive microflora, physiological history, and surface transfer. To develop novel approaches to assess model performance and robustness, leading to more efficient strategies for producing and extrapolating models to different classes of food. To determine the probability distribution of lag phase duration (LPD) for foodborne pathogens, as a function of the previous bacterial physiological history, to allow risk managers to estimate worst-and best-case scenarios for pathogen behavior, depending on likely sources of contamination; To identify molecular markers that discriminate bacterial lag, growth and stationary phases, thus leading to more mechanistic models and greater certainty for LPD prediction.

1b.Approach (from AD-416)
Quantitative data will be collected for the effects of selected environmental parameters on foodborne pathogen growth, survival and inactivation. Relevant environmental conditions will include food formulation, native microbial flora, inoculum level, bacterial history, and the effects of food process operations. Priority pathogen-food combinations will be identified through stakeholder interactions and by identifying sensitive data gaps in microbial risk assessment. Experimental data will be used to confirm and where necessary produce primary growth and inactivation models, as well as probabilistic models for growth/no growth interfaces and microbial transfer among food processing surfaces. Model performance will be described using independent validation data from ongoing experiments with food matrices and microbiology databases such as ComBase. The resulting technologies will be transferred to stakeholders vis the ARS Pathogen Modeling Program and process risk model software.

3.Progress Report
Mathematical equations for description the growth, survival or inactivation of L. monocytogenes in smoking process,in cooked ham, and in ham, egg, pasta, and potato salads were developed into Excel models. All data were formatted in Excel spreadsheet for Combase submission.

A series of experiments were conducted to determine the germination and outgrowth of Clostridium perfringens spores during cooling of cooked pork products. Predictive model for growth of Clostridium perfringens during cooling of cooked pork products based on the product composition factors is being developed. The growth data /predictive models on the safe cooling rate of meat will enable the food industry to assure that cooked products remain pathogen-free.

Data were collected in a series of experiments with chicken meats (white and dark meat) and other initial doses of Salmonella and with Salmonella on chicken skin that was frozen for one week. These data indicated that the model did not provide acceptable predictions of Salmonella growth and survival on chicken skin when other initial doses of the pathogen were present but that the model did provide acceptable predictions of Salmonella growth and survival on chicken skin when the pathogen was subjected to a previous history of freezing for one week before the experiment. These results indicate that the model should be expanded to include other initial doses of Salmonella. This expanded model will provide the chicken industry and regulators with an improved predictive tool for assessing and managing this risk to public health.

Experiments were conducted to determine the impact of prior history on the lag phase duration of L. monocytogenes and Escherichia coli O157:H7. The pathogens were exposed to 25 - 75ppm chlorine for 1 h prior to assessing the lag phase of 3 – 4 log CFU/g cells on sliced ham at temperatures ranging from 4 – 24C. While lag phase of L. monocytogenes varied considerably, E. coli O157:H7 lag phase was longer after exposure to higher chlorine concentration and at lower incubation temperatures. Models to predict the lag time and growth rate were developed and validated. A series of experiments were conducted to study the growth of Y. pestis ranging from 0-30C in pork and also to investigate the stability of virulent plasmid during its growth in ground pork. Yersinia pestis grew at storage temperatures from 10-30C and reached maximum population density. The virulence plasmid was retained in Y. pestis in ground pork. stored at refrigerator temperatures or during its growth at 10-30C. The fate of RpoS, an alternate sigma factor responsible for regulating many of the genes responsible for survival of bacteria, in the transition from stationary phase to lag phase growth using Escherichia coli O157:H7 as a model strain was studied. To verify that E. coli O157:H7 (EDL933 and Sakai strains) expressed a full length version of RpoS, the DNA sequence of this gene in EDL933 and Sakai strains has been initiated and the sequence data are being generated.

1. Proper means for cooling of cooked beef. Inadequate rate and extent of cooling of cooked foods is a major food safety problem. ARS scientists in (Wyndmoor, PA), determined the germination and outgrowth of Clostridium perfringens spores during cooling of cooked beef products. Predictive model for growth of Clostridium perfringens during cooling of cooked beef products based on the product composition factors was developed. The growth data /predictive models on the safe cooling rate of meat will provide the food industry means to assure that cooked products remain pathogen-free.

2. Predictive model for L. monocytogenes in ready-to-eat (RTE) meat. L. monocytogenes is pathogen commonly associated with foodborne illness caused by consumption of contaminated ready-to-eat meat. ARS scientists in (Wyndmoor, PA) developed models to describe the survival and growth of L. monocytogenes and native microflora in ready-to-eat ham. Excel models for L. monocytogenes in smoking process, in cooked ham, in ham, egg, pasta, and potato salads were posted on ERRC-ARS website. The models will help the manufacturers to determine the effect of temperature changes during distribution and storage of ham on the safety and quality of their products.

3. Transfer of pathogens during mechanical slicing of deli meats. Food safety managers currently lack the ability to predict the microbial pathogen transfer in slicing operation for ready-to-eat (RTE) foods. Models were developed by ARS scientists in (Wyndmoor, PA) for pathogen transfer prediction during mechanical slicing for RTE deli meats. The shear stress may reduce a large amount (99%) of pathogens, such as Listeria monocytogenes, as demonstrated using confocal microscopy. Predictive models will be useful for food manufacturers in developing Hazard Analysis Critical Control Points (HACCP) plans and in risk assessments for RTE meats.

4. Chemical hurdle for improved food safety. Listeria monocytogenes is an opportunistic human bacterial pathogen of food origin that causes illness in certain at risk groups, such as pregnant women, newborn babies and adults with underlying health problems. Due to the high case-fatality rate (20%), development of control measures for this pathogen is of major interest to the food industry. In collaboration with university scientists, ARS scientists in Princess Anne, MD demonstrated that a commercial formulation (Purasol P Opti.Form 4TM) of organic acid salts (sodium and potassium lactate and sodium diacetate), which are recognized as safe food additives, exhibited pronounced inhibition of the pathogen in broth formulations that simulated meat and poultry products stored at cold temperatures. The resulting predictive model can be used to design a substantial chemical hurdle to the survival and outgrowth of Listeria monocytogenes in meat and poultry products stored at a range of temperatures.

5. Use of marinade to guard against Salmonella problems. Salmonella contamination of chicken is a major public health problem throughout the world. Soaking chicken in a marinade before cooking to impart a unique flavor is a common practice. Some marinades contain ingredients, such as vinegar and spices, which can reduce or eliminate human pathogens like Salmonella. In collaboration with a university scientist, ARS scientists in Princess Anne, MD found that overnight cold storage of chicken in an Italian-style marinade, which contained vinegar and spices, greatly reduced Salmonella levels making it a simple and low cost method that consumers can use to improve not only the flavor but also the safety of chicken for their families.

6. Not all Salmonella are created equal. Chickens from a commercial processing plant were found to be contaminated most often with one of two types of Salmonella: Typhimurium or Kentucky. Salmonella Kentucky is rarely found in human clinical cases of foodborne illness, whereas Salmonella Typhimurium is often found in such cases. ARS scientists in Princess Anne, MD discovered that Salmonella Kentucky grows much slower on chicken than Salmonella Typhimurium, which may explain why it rarely causes illness in humans. They also developed a computer model that predicts the difference in risk to humans of chicken contaminated with these two types of Salmonella. The model is projected to save the chicken industry and consumers millions of dollars per year by better predicting chicken safety.

7. Virulent plasmid stability of Yersinia pestis in ground beef. To fully assess the potential risk of illness, ARS scientist (Wyndmoor, PA) determined the stability of the virulent plasmid in Y. pestis during its growth in raw ground beef. The virulence-associated plasmid was retained in Y. pestis during its growth in ground pork and therefore, pork contaminated with Y. pestis could cause disease due to refrigeration failure, temperature abuse (10-25C), and improper cooling. The resultant disease may lead to outbreaks of highly infectious pneumonic plague. Understanding on the growth behavior of the pathogen will reduce the uncertainty in risk assessments designed to manage threats to the US food supply and provide risk managers with greater certainty in estimating the impact of Y. pestis in the safety of food.

5.Significant Activities that Support Special Target Populations
ARS operates a USDA/1890 Center of Excellence Program at University of Maryland Eastern Shore in Princess Anne, MD that specifically targets a minority, historically underserved group (African Americans) for careers in agriculture. Activities this year included:.
1)service on six graduate student committees;.
2)two guest lectures in a graduate level food science class;.
3)and provision of research experiences and training in predictive microbiology for three undergraduate and four graduate students.

Review Publications
Juneja, V.K., Porto Fett, A.C., Call, J.E., Marks, H., Tamplin, M., Luchansky, J.B. 2010. Thermal inactivation of Bacillus anthracis Sterne in irradiated ground beef heated in a water bath or cooked on commercial grills. Innovative Food Science and Emerging Technologies. 11:123-129.

Sheen, S., Hwang, C. 2010. Mathematical modeling the cross-contamination of Escherichia coli O157:H7 on the surface of ready-to-eat meat product while slicing. Food Microbiology. 27:37-43.

Juneja, V.K., Marks, H.L., Thippareddi, H. 2010. Predictive model for growth of Clostridium perfringens during cooling of cooked ground pork. Innovative Food Science & Emerging Technologies. 11:146-154.

Maks, N., Zhu, L., Juneja, V.K., Ravishankar, S. 2010. Sodium lactate, sodium diacetate and pediocin: effects and interactions on the thermal inactivation of Listeria monocytogenes on bologna. Food Microbiology. 27:64-69.

Bhaduri, S. 2010. Effect of fat in ground beef on the growth and virulence plasmid (pYV) stability in Yersinia pestis. International Journal of Food Microbiology. 136:372-375.

Hwang, C. 2010. Delicatessen salads in "refrigerated ready-to-eat foods: microbial concerns and control measures". In: Hwang, C.A., Huang, L., editors.Ready-to-Eat-Foods: Microbial Concerns and Control Measures. New York, NY: CRC Press. p. 61-80.

Hwang, C., Sheen, S., Juneja, V.K. 2009. Effect of salt, smoke compound and temperature on the survival of Listeria monocytogenes in salmon during simulated smoking processes. Journal of Food Science. 74(9):M522:M529.

Juneja, V.K., Hwang, C., Friedman, M. 2010. Thermal inactivation and post-treatment growth during storage of multiple Salmonella serotypes in ground beef as affected by sodium lactate and oregano oil. Journal of Food Science. 75(1):M1-M6.

Juneja, V.K., Porto Fett, A.C., Gartner, K., Tuft, L., Luchansky, J.B. 2010. Potential for growth of Clostridium perfringens from spores in pork scrapple during cooling. Foodborne Pathogens and Disease. 7(2)153-157.

Oscar, T.P. 2009. General regression neural network and Monte Carlo simulation model for survival and growth of Salmonella on raw chicken skin as a function of serotype, temperature and time for use in risk assessment. Journal of Food Protection. 72(10):2078-2087.

Abou-Zeid, K.A., Yoon,, K.S., Oscar, T.P., Whiting, R.C. 2009. Development and Validation of a Predictive model for Listeria monocytogenes Scott A as a function of Temperature, pH and Lactate and Diacetate Mixture. Journal of Microbiology and Biotechnology. 19(7):718-726.

Oscar, T.P., Singh, M. 2009. Persistance of Salmonells spp. on Chicken Skin after Exposure to an Italian Marinade. Journal of Rapid Methods and Automation in Microbiology. 17(3):369-382.

Last Modified: 10/9/2015
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