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Introduction
The ARS Food Safety Program seeks to reduce to the greatest extent possible the incidence of food borne illness, and addresses the production, harvesting, processing, transportation, handling, and storage of food (the farm to table continuum) and emphasizes the prevention and/or control of food pathogens. Food may unintentionally contain contaminants, either toxic chemicals or toxins of natural origin. The Program also seeks to address the prevention of toxic chemical hazards in food: that is, mycotoxins, drug and environmental chemical residues, and toxic plants, through cost effective research programs that maximize benefits to public health and returns-on-investment, to producers, processors, and the public.
The ARS food safety program is flexible, and can be quickly redirected to address new and emerging issues when necessary from its core of expert scientists. ARS provides practical solutions for producers and works closely with their commodity organizations to prevent and eliminate food safety problems. ARS coordinates their food safety research to meet the needs of the Federal action and regulatory agencies, in particular the USDA-Food Safety and Inspection Service, and the FDA-Center for Food Safety and Nutrition.
The budget for the ARS Food Safety research program remained relatively constant in 2002. An increase of $216,000 for postharvest research brought the total funds to $93.32 million, $55.15 million for preharvest and $37.17 million for postharvest. The new postharvest funds were directed for research on Listeria monocytogenes and Escherichia coli O157:H7.
During 2002, collaborative research programs were continued with the National Alliance for Food Safety to specifically address issues relative to pathogen reduction. Funded projects focused on: robustness of predictive models for Listeria growth and inactivation in ready-to-eat meat and poultry products; role of nematodes in preharvest contamination of fresh fruit and vegetables; construction of microarrays for E. coli O157:H7; investigating the transmission dynamics of antimicrobial resistance in integrated animal and human populations using molecular epidemiology; effects of cool water washing of shell eggs on microbiological, interior quality and environmental characteristics; and molecular ecology of Listeria, Salmonella and Campylobacter in the turkey processing industry.
Collaborative Postharvest research programs continued with The Institute for Genomic Research (TIGR) to provide annotated genomic sequences of the bacterial pathogens Listeria monocytogenes and Campylobacter jejuni.
Each program was expanded during 2002 to include sequencing at least 3 additional strains of each pathogen. The Postharvest program also initiated a research project with Lawrence Livermore National Laboratories in California to determine signature sequences that could be used to identify and differentiate Listeria serotypes and strains. Each year ARS sponsors, leads and/or participates in national and international food safety meeting/workshops. In 2002, several workshops were conducted to convey research progress to customers and stakeholders. The Annual ARS-FSIS Research Program Planning Meeting, held in Williamsburg, VA, brought together ARS scientists and FSIS staff for a research progress update, and discussion of FSIS needs for meeting their regulatory responsibilities. Representatives from several other federal agencies with food safety programs also participated; for example, the USDA-CSREES, FDA-CFSAN, Canadian Food Inspection Agency, Health Canada, Institute Food Research, Norwich, UK, and the UK-Food Standards Agency.
The Annual Aflatoxin Elimination Workshop, held in San Antonio, TX, updated the peanut, corn, cottonseed and tree nut industries on ARS supported research progress made to control aflatoxin and fumonisins in these commodities. The Annual Fresh Fruit and Vegetable Research Planning Workshop, held at National Program Staff, Beltsville, MD, brought together ARS scientists, FDA-CFSAN scientists and staff, and University collaborators for a research progress update, and discussion of FDA needs for meeting their regulatory responsibilities.
The Preharvest program held a Workshop at National Program Staff with the Regional Dairy Quality Management Alliance to discuss validation of Dairy better management practices.
A joint ARS-IFR-FSA (Institute of Food Research-BBSRC, Norwich, UK; UK Food Standards Agency Workshop was held in March in London, UK, to identify Postharvest program areas for collaboration between ARS and scientists within the European Union (EU). Major actions resulting from the meeting were the establishment of an MOU between ARS and the IFR, and continued agreement to expand the cooperative research programs between ARS and IFR.
Two joint National Program 107 and 108 (Nutrition, and Food Safety) and Tekes (National Technology Agency of Finland) meetings, and a joint ARS (NP 107/108/306)-Tekes Workshop were held in Finland, in February, March and August respectively to identify specific Nutrition-Postharvest Food Safety and Food Quality program areas for collaboration between ARS, and scientists within Finland. Major actions resulting from the meeting were the establishment of an MOU between ARS and Tekes. Several cooperative research programs between ARS and Finnish scientists have begun.
The Postharvest research program started several joint international research initiatives with the DG-12 Section of the EC in Brussels who funded two multi-institutional projects through the European Commissions-Framework- 5. The projects with various universities, research institutes, government agencies, and industry are focused on: developing microbial methods for detection and differentiation of Campylobacter species; and collation and management of data for risk modeling.
In 2002, several remaining research (CRIS) projects within the Food Safety Program underwent external review through the OSQR (Office Scientific Quality Review) process. A peer review panel comprised of scientific peers with expert knowledge of the fields of science pertinent to the research being reviewed provided an in-depth critique of research project plans. The review criteria and project plan design policies assure that ARS research scientists develop carefully conceived project plans that focus on three key elements of research planning: merit and significance as it aligns with the Program Action Plan; approach and procedures; and probability of success.
Microbial Pathogens
Determining how to reduce microbial pathogens in food products, throughout food operations from farm to fork, is the most urgent food safety problem today. The major pathogens addressed were the bacterial pathogens Salmonella, Campylobacter, E. coli 0157:H7 and related EHEC, Shigella, Listeria, Yersinia, Aeromonas, Arcobacter, Vibrio and Clostridium; the parasites Cryptosporidium and Toxoplasma; and various viruses, hepatitis A Norwalk and Norwalk-like viruses and rotavirus.
E. Coli O157:H7 found on animal skin and the oral cavity, and killed by sodium chlorate. The pathogen of greatest concern to the safety of animal based foods is E. coli O157:H7, and it is primarily a problem of cattle and beef. ARS scientists in Clay Center, NE, demonstrated that the hide surface and the oral cavity of finished beef feedlot cattle usually have a higher E. coli O157:H7 prevalence than do bovine feces. This finding may help to explain several recent outbreaks of this pathogen in children following farm tours and visits to county fairs. Another ARS laboratory in College Station, TX, developed workable protocols for administration and evaluation of a new pathogen control compound to beef and dairy cattle just prior to slaughter. Specially formulated sodium chlorate preparations administered in feed an/or drinking water just days prior to slaughter selectively killed pathogenic E coli and Salmonella in the animal's gut, reduced hide and carcass contamination with these pathogens, and had no negative effects on final product quality. This will provide a practical efficacious, cost-effective and commercially viable product that significantly enhances the microbiological safety of beef food products.
Microsporidia, an emerging human pathogen, found in cattle and wildlife. To assess the potential for cattle and aquatic mammals to serve as reservoirs of pathogenic microsporidia parasites, ARS scientists in Beltsville, MD, developed diagnostic assays and tested cattle fecal samples from MD, PA, VA, and FL, and aquatic wildlife fecal samples from around the Chesapeake Bay. Several species of microsporidia were identified in cattle in 3 of the 4 states. The same microsporidia was also identified in fecal samples collected from muskrat, beaver, otter, raccoon and fox. This is the first finding of this organism in cattle in North America and in wildlife worldwide, and it identifies these animals as potential sources of an emerging human pathogen, thus providing direction for further research to protect the food supply.
Salmonella proteins identified as targets for inhibition by antibiotics. The acquisition of antibiotic resistance and/or enhanced virulence by bacterial pathogens is a threat to human health and we need methods to mitigate this resistance. Using a novel genetic system and high-throughput screening assays an ARS laboratory in Ames, IA, identified six Salmonella proteins that are essential for growth, virulence or antibiotic resistance. Identifying specific proteins and their functions will provide research directions to understand the antibiotic resistance and prevent its spread and acquisition by other bacteria and other hosts.
Assays developed to accurately classify and identify Enterococci. Accurate classification of bacterial pathogens is necessary to trace their movement through natural and manmade environments. The current classification and identification scheme for Enterococcus, based on phenotypic analysis, is both tedious and laborious, requiring at least 24 hours. ARS scientists in Athens, GA, developed a DNA based assay that will identify the genus and species of 19 of 25 Enterococcus strains that have been isolated and classified. From start to finish the entire process is cost effective, rapid and accurate, and requires approximately 3 and one half hours. This classification process will help establish a firm basis for antibiotic use recommendation to decrease pathogen resistance to drugs.
Potential for bacterial regrowth demonstrated in treated, reclaimed water. In water-short areas reclaimed water must be used for agricultural or other approved uses, and its potential for bacterial regrowth in reclaimed water used for crop irrigation must be understood. ARS scientists in Phoenix, AZ, assessed the survival and regrowth potential of bacteria present in tertiary-treated effluent used for crop irrigation and surface water discharge as it passed through a model laboratory distribution system. Total bacteria increased 3 to 4 orders of magnitude, and that E. coli remained viable during the 11-day experiment. This research has established that although the reclaimed water met EPA standards for irrigation at the wastewater treatment plant, there is great potential for bacterial regrowth during transport that could place the water out of compliance at the point of intended use. The information will help prevent future problems of food contamination via wastewater irrigation.
Risk of pathogens in ground beef. Contamination of ground beef by E. coli O157:H7 is a critical issue for regulatory-action agencies, industry and consumers. In order to better assess the risk for contamination, ARS scientists at the Eastern Regional Research Center in Wyndmoor, PA, developed mathematical models to estimate the effects of grinding processes on the distribution of E. coli O157:H7. Beef trim contaminated with E. coli O157:H7 was processed similarly to that done by industry to produce a ground product. The research showed that there are defined distribution patterns at different levels of contamination, and showed that the pathogen accumulates and resides in selected components of the grinder. These results will greatly assist in reducing the uncertainty of how beef is contaminated at the grinding process step, and will also assist in designing improved sanitation and microbiological sampling procedures.
New technology for killing pathogens in molluscan shellfish. A large number of viruses can cause sickness and/or death among consumers who eat raw or lightly cooked molluscan shellfish. ARS scientists at Delaware State University showed that Hepatitis A virus and Calicivirus in oysters could be killed using high pressure processing techniques. This technology could readily be implemented by industry to provide consumers with a safe product that could be eaten raw.
Contamination of ready-to-eat foods by Listeria. The number of recalls of ready-to-eat foods such as hot-dogs due to contamination by Listeria has dramatically increased during the past few years. ARS scientists at the Eastern Regional Research Center in Wyndmoor, PA, in association with industry, conducted a study to assess the prevalence of Listeria monocytogenes in commercially produced, vacuum-sealed packages of hot-dogs from 12 different volunteer manufacturers, in 10 U.S. States. In total, 1.6% of the 33,000 sampled packages tested statistically positive for the pathogen. There was no appreciable difference in recovery rate of the pathogen due to time, or storage at either 4 or 10 degrees C, the latter being the temperature of most household refrigerators. Seasonality of manufacture, for example, summer versus winter also had no influence. This baseline-data on prevalence is critical for industry and regulatory-action agencies in developing guidelines for setting a safe shelf life for hot-dogs relative to the risk of listeriosis, and/or for recommending conditions for heating hot-dogs prior to consumption.
Salmonella contamination of produce. Cantaloupe has been implicated in several major Salmonella outbreaks during the past 3 years, which has led to the FDA now recommending that customs officials halt the import of all cantaloupes from Mexico. ARS scientists at the Eastern Regional Research Center in Wyndmoor, PA, investigated why Salmonella contamination persists on the product. Studies with various pathogens demonstrated that Salmonella bacteria due to its chemical structure attached more strongly to the cantaloupe rind than other pathogens, making it more resistant to treatment with sanitizers. These findings may explain why salmonellosis is the primary foodborne illness associated with the consumption of fresh-cut melons, and indicates that a more effective means of either detaching or killing the attached bacteria are required to help ensure the safety of this product for the consumer.
Method for identifying Listeria. Rapid, easy, cost effective, and correct identification of bacterial pathogens is critically important for regulatory-action agencies and industry. ARS scientists at the Western Regional Research Center in Albany, CA, developed a accurate, rapid, reproducible, cost effective method for typing Listeria monocytogenes strains using commercially prepared components, at a sensitivity level 1000-fold better than currently used. The method was tested on over 100 reference and unknown strains, and proved highly accurate. The new method will have a significant impact on the ability to rapidly detect and characterize Listeria monoctyogenes from food products.
Cleaning-up water and manure. Huge manure production by large livestock production practices, especially concentrated operations, has led to significant environmental problems from excess nutrient availability, and manure as a frequent route of contamination of produce. ARS scientists at the Western Regional Research Center in Albany, CA, have developed an electroflotation device that disinfects fluids while physically entrapping and removing insoluble and soluble solids. The technology was tested on manure water from a dairy farm operation, and demonstrated that it could reduce some bacteria by nearly one-hundred-million-fold, while reducing total suspended solids by 95%. The technology could have a significant impact since it could potentially be used to treat manure for safe disposal or application on crops without health and environmental concerns.
Importance of pathogens closely related to E. coli O175:H7. No information concerning the prevalence or virulence of pathogenic non-O157 Shiga toxin-producing E. coli (STEC) in beef cattle is currently available. ARS scientists from the Meat Animal Research Center in Clay Center, NE, sampled carcasses at four large beef processing plants in the United States for non-O157 STEC's and found a prevalence of greater than 50% on beef carcasses prior to evisceration during processing. The levels on carcasses were however, reduced to 8.3% by in-plant antimicrobial interventions. Subsequently, non-O157 STEC, possessing accessory virulence factors indicative of pathogenic strains, were identified on only two carcasses (0.6%) at postprocessing. This is the first comprehensive study of its type, and will provide regulatory-action agencies and industry with information to be used in establishing baseline prevalence levels.
New coating to reduce pathogens in poultry. Development of successful intervention strategies are urgently needed in order to reduce the level of bacterial pathogens associated with poultry products. ARS scientists at the Richard Russell Research Center in Athens, GA, in association with industry and commercial partners evaluated a new Generally Recognized As Safe (GRAS) calcium-based compound. The GRAS-compound demonstrated the ability to reduce Salmonella, Campylobacter and E. coli pathogens to levels equivalent to treatment with Tri-Sodium-Phosphate (TSP), and also increase the shelf life of carcasses. Due in-part to the ARS research results, the GRAS-compound has been approved by the Food Safety Inspection Service as an in-plant, pre-chill treatment for broiler carcasses. On-going commercial studies should demonstrate and confirm that this product will deliver a microbiologically safer product to the consumer with less environmental impact.
Chemical Residues
The objectives of the chemical residue program are to reduce the risks of chemical residues from animal drugs, food additives, herbicides and pesticides and environmental contaminants that are potentially present in foods. A major goal is to develop reliable, effective, accurate, user-friendly, cost-effective residue detection methodology that requires minimal amounts of organic solvents to detect these residues.
Degradation of hormones in manure. The endogenous hormones, estradiol and testosterone which are produced by all animals, are found in animal manure particularly from concentrated animal feeding operations and may pose a threat to human health through their contamination of surface and ground waters. ARS scientists in Fargo, ND, determined the degradation rate of these hormones during composting of manure. Initial concentrations of testosterone and estradiol in chicken manure averaged 212 and 92 parts per billion (ppb), respectively, but fell gradually over 129 weeks to 13 ppb for testosterone and 16 ppb for estradiol. The rate of degradation of testosterone was 3 times that of estradiol. Thus composting may be an environmentally friendly technology suitable for reducing the amounts of the endogenous hormones at concentrated animal operation facilities, thus preventing their transport into surface or groundwater systems that could be a source of drinking water.
New technology for detection of pesticides in foods. Industry, as well as regulatory-action agencies in the United States and worldwide, needs improved cost effective methods to detect pesticides in agricultural commodities. A new, quick, easy, cheap, effective, rugged, and safe method called QuEChERS (pronounced "catchers") was developed by ARS scientists at the Eastern Regional Research Center in Wyndmoor, PA. The new method provides high quality results for a wide range of pesticides. Using the method, a single technician can prepare 12 samples in less than 30 minutes for about $10, using a single piece of reusable glassware. This new technology will have a significant national and international impact on monitoring the food supply for harmful and illegal pesticides.
Mycotoxins
The presence and potential for the presence of mycotoxins in crops is not only a direct food safety problem but it threatens the competitiveness of U.S. agriculture in the world market. Major goals are to control aflatoxin in peanuts, corn, cottonseed, tree nuts and figs; fumonisins in corn; and deoxynivalenol in wheat and barley through an understanding of the biology of plant-fungus interactions and toxin production in the field.
Potent natural inhibitor of aflatoxin formation found in tree nuts. Contamination of tree nuts by aflatoxins produced from infection by the fungus Aspergillus flavus and A. parasiticus is a serious problem because of the stringent regulatory levels imposed for these toxins and the potential threat to human health. ARS scientists in Albany, CA, demonstrated that the sources of the high aflatoxin resistance of the seed coat pellicle of the Tulare variety of walnut is a series of complex, structurally related polar compounds of which gallic acid is a major component. ARS scientists demonstrated that gallic acid is a potent inhibitor of aflatoxin synthesis when the fungus is exposed to these compounds. Measurement of gallic acid levels in different tree nuts will provide a means of assessing the aflatoxin resistance of individual varieties that will result in lesser amounts of aflatoxin in tree nuts and greater protection of the public health.
Timing of aflatoxin production in cottonseed. The occurrence of aflatoxin severely limits the value of cottonseed, an economically important byproduct of cotton production in Texas. An ARS scientist in New Orleans, LA, identified the importance of the second (post maturity) phase of aflatoxin contamination of cottonseed that occurs when exposure of mature bolls to high humidity and temperature and rainfall stimulates crop invasion by aflatoxin producing fungi. Recognition of these key features may allow identification of predisposing environmental and agronomic factors, and as a result, improved management recommendations can be made to prevent the occurrence of aflatoxin. This will increase the safety of cottonseed in human and animal food and increase the return to growers.
Gene identification can help to eliminate aflatoxin formation. Aflatoxins produced by the fungus Aspergillus flavus can infect crops, such as corn, cotton, peanuts and treenuts causing a potential food safety hazard and lowering their economic value. ARS scientists in New Orleans, LA, prepared a cloned genetic library of the aflatoxigenic fungus. The DNA of each of these clones was sequenced, in collaboration with TIGR, to identify unique genes that the fungus uses to accomplish all of its biological and physiological functions. These scientists have also begun to profile all the genes that are functional and active during both fungal invasion of the crops and aflatoxin formation, thus providing the basis for understanding how aflatoxin is formed in crops and deciphering how environmental factors affect the fungus. This information will help devise effective and lasting strategies to modulate or control aflatoxin formation.
Toxic Plants
This program component seeks to minimize the exposure of animals and humans to natural toxins from poisonous plants.
Sound basis developed for establishing cadmium levels in US commodities. International sales of US crops would be limited by international limits on cadmium in edible grains. Such limits require that the amounts of cadmium reaching internal tissues be considered, rather than only the amounts in the diet. ARS scientists at Beltsville, MD, collaborated with scientists in Grand Forks, ND, to measure rice diet cadmium uptake and excretion by different segments of the small intestine of rats. The very high absorption of cadmium in these animals receiving the marginal iron, zinc and calcium in this rice diet was to cells lining intestine, however, the prolonged period in which absorbed cadmium remained in these cells allowed much higher absorption to internal tissues over time than if the cadmium were excreted with the contents of the meal under test. This information will allow more accurate estimations of the bioavailability of cadmium, thus greatly lowering concern about dietary cadmium for foods other than rice, and decreasing potential difficulties with export of US foods while at the same time protecting the public health.
Rapid tests for plant toxins help livestock producers avoid losses. Grazing of ponderosa pine needles causes abortion/premature parturition, retained placentas and endometritis in pregnant cattle resulting in substantial economic losses to cattle producers in the western US. ARS scientists in Logan, Utah, developed rapid test (ELISAs) for isocupressic acid (ICA) and its metabolites using polyclonal antibodies. Similarly, assays were developed to detect and measure two significant teratogenic steroidal alkaloids in Veratrum plant species, as well the photosensitivity agent, phylloerythrin. These assays to rapidly screen biological samples for the presence of these toxins will help speed further research to find the ultimate cause of both reproductive failures and photosensitivity, and/or will ultimately aid ranchers in identifying areas to avoid grazing by susceptible animals.
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