Concern over food safety puts focus on pathogens

Transcription

1 Concern over food safety puts focus on pathogens By Kasey M. Herbst Issue Number 53 November 1994 FOOD SCIENCE N EWSLETTER Bacteria, viruses, fungi, protozoa, and other microscopic parasites have ample opportunity to contaminate our food before we eat it. When ingested, some of these microorganisms, or the toxins they produce, can cause gastrointestinal distress or more serious illnesses. Recent publicity has brought renewed attention to some well-known pathogens in food, including Salmonella and Shigella, and spotlighted less familiar ones such as Escherichia coli O157:H7, Listeria, and Vibrio. Meanwhile, additional microorganisms, and more virulent forms of known pathogens, continue to be discovered. Old and new pathogens alike will test the prevention strategies of food-safety regulators in this country and around the world. Recent outbreaks reveal that foodborne diseases constitute a significant, perhaps intensifying, problem in the United States. Hundreds of passengers and crew on a Los Angeles to Mexico cruise earlier this year were infected with Shigella. In April, two dozen people in Texas were hospitalized with botulism, apparently originating in a dip made from potatoes that had been left unrefrigerated for 18 hours after baking. A number of recent deaths have been attributed to Vibrio vulnificus, a bacterium found in shellfish harvested from the Gulf of Mexico in the summer months. In 1993, E. coli O157:H7 in undercooked hamburgers from fast-food restaurants was responsible for three deaths and hundreds of cases of food poisoning in the Pacific Northwest. Sources of foodborne illnesses Some of the most serious cases of foodborne illness have involved restaurants. In the U.S., the number of fast-food restaurants alone has soared from 70,000 two decades ago to 150,000 today. The popularity of dining out has increased the potential for encountering food that has been contaminated in the course of handling by suppliers, kitchen personnel, and serving staff. Restaurants and other food service operations have been implicated in some 70% of reported outbreaks of foodborne illness. Avoiding restaurants does not guarantee safe food, however. Food prepared in home kitchens is linked with 20% of reported cases of illness involving food. Many experts feel that safe handling and preparation of food are being neglected at home as the general population increasingly takes food safety for granted. A new label required on raw meat sold in the U.S. is designed to improve this situation by providing information on safe handling and proper cooking of meat in the home. Problems in food handling and preparation extend to other segments of society as well. The food processing industry is involved in 10% of reported cases of foodborne illness, often occurring when controls break down or are not maintained. In October, thousands of people in 35 states were made sick by Salmonella that got into ice cream produced at a plant in Minnesota. The contamination is thought to have originated from a previous shipment of raw unpasteurized eggs on the same truck that later carried the ice cream mix to the packing plant. The type of backhauling that led to the Salmonella contamination would have been halted under regulations proposed by the Department of Transportation (DOT) in DOT also issued a proposed regulation on sanitary food transportation in 1993, but neither rule was ever finalized. 1

2 Complacency, perhaps in the belief by the public that food safety is a solved problem, has contributed significantly to the hazard of foodborne illness. And this comes at a time when an aging population and an increased incidence of immune deficiency are putting more people at risk from foodborne pathogens. Adding to the potential risk are growing consumer demands for foods with low levels of microbial inhibitors; refrigerated, ready-to-eat foods with extended shelf-life (during which time pathogenic microbes may proliferate); fresh and processed foods from around the world; and undercooked or uncooked meat and fish. Because most cases are not reported, a firm accounting cannot be made of how many people contract foodborne illnesses. A task force of the Council for Agricultural Science and Technology recently estimated the number of such cases each year in the U.S. to be between 6.5 million and 33 million, up to 9,000 of which lead to death. Worldwide, some 300 cases of acute gastroenteritis occur each year per 1,000 persons, with up to 50% of these disorders caused by foodborne and waterborne microorganisms. The major pathogens in food Bacteria and other pathogenic microorganisms in food cause illness in humans by direct infection or through the actions of toxins produced before or after food is ingested. Viruses act by direct infection. The most serious viruses encountered in food are hepatitis A virus (HAV) and Norwalk-type viruses. These can occur in prepared food handled by infected workers. In the mid-1980s, HAV and Norwalk were among the top ten identified causes of foodborne illness in the U.S. Protozoa and other parasitic pathogens in foods produce direct infections in their victims. Cryptosporidium, which rose to notoriety in 1993 as a waterborne infection causing moderate to severe diarrhea, is also found in marine fish and possibly in raw milk and raw vegetables. Mycotoxins are toxins generated by fungal pathogens in food. The most prominent mycotoxin is aflatoxin, produced by the mold genus Aspergillus. Some forms of aflatoxin are extremely toxic to humans as well as being the most carcinogenic natural compound. Although many kinds of pathogenic microorganisms exist in food products, fungi and bacteria are the only ones that can multiply in food. Some dangerous bacteria, such as Listeria monocytogenes and Yersinia enterocolitica, can grow even when food is properly refrigerated for long periods. Most bacteria that directly infect humans are killed by proper cooking of foods, although some pathogenic bacteria form spores that can survive boiling or chemical cleansing treatments. Many toxins can also withstand boiling. Salmonella is the pathogen most frequently associated with foodborne illness in the U.S. and in most other developed countries. This bacterium, which causes direct infection, is found in meat, fish, and dairy products; some studies have indicated that 25% of broiler chicken carcasses in the U.S. are contaminated with Salmonella. Shigella is another genus of foodborne bacteria that act by direct infection. A number of foodborne bacteria that cause direct infections in the U.S. have been recognized as important pathogens only in the last two decades; these include Campylobacter jejuni, E. coli O157:H7, Listeria monocytogenes, Vibrio spp., and Yersinia enterocolitica. Toxins produced by Staphylococcus aureus result in the second greatest number of reported foodborne illnesses in the U.S. Bacteria that produce the toxins can occur in cooked meat that has been handled and then is not properly refrigerated. Among other toxinproducing bacteria known to cause foodborne illnesses in the U.S. are Bacillus cereus, Clostridium botulinum, Clostridium perfringens, and Vibrio cholerae. The regulatory situation Because they can cause serious illness in persons with compromised immune systems, certain bacteria, including Listeria monocytogenes and Salmonella, are not permitted to be present in any processed, readyto-eat foods in the U.S. A recent and controversial policy change has put E. coli O157:H7 under the tightest control of any foodborne bacterium. E. coli O157:H7 has only recently been recognized as a pathogen; most other strains of E. coli are less virulent. In October, the Food Safety and Inspection Service (FSIS), a branch of the U.S. Department of Agriculture (USDA), began testing ground beef for the deadly E. coli strain, which is associated with life-threatening illness due 2

3 The dangers and sources of some important foodborne pathogens Type of organism Severity of hazard Implicated sources to humans of contamination Bacteria Bacillus cereus Mild to moderate Rice, pasta, beef, dairy products Campylobacter jejuni Mild to moderate Poultry, beef, pork, eggs, raw milk Clostridium botulinum Severe Improperly canned low-acid foods; improperly handled vegetables and meat Clostridium perfringens Mild to moderate Meats, poultry Escherichia coli O157:H7 Moderate to severe Raw ground beef, other meats, poultry Listeria monocytogenes Mild to severe Meats, poultry, seafood, dairy products Salmonella spp. Mild to severe Meats, poultry, shellfish, raw milk Shigella spp. Moderate to severe Improperly handled food; drinking water Staphylococcus aureus Mild to severe Unrefrigerated meats, poultry, seafood, salads, pastries Vibrio vulnificus Severe Raw oysters Vibrio parahaemolyticus Mild to moderate Seafood Vibrio cholerae Moderate to severe Seafood Yersinia enterocolitica Mild to moderate Pork, milk, raw vegetables Viruses Hepatitis A Moderate to severe Improperly handled food Norwalk and Norwalk-like Mild to moderate Improperly handled food Fungus Aspergillus spp. Potentially severe Peanuts, rice, corn, wheat Parasitic protozoa Cryptosporidium parvum Moderate to severe Fish, drinking water; possibly raw milk and raw vegetables Giardia lamblia Mild to moderate Drinking water Toxoplasma gondii Mild to severe Pork, ground beef Other parasites Taenia spp. Mild to severe Beef, pork Trichinella spiralis Moderate to severe Undercooked pork Adapted from: Pierson & Corlett 1992 and CAST

4 to eating undercooked beef. E. coli O157:H7 is normally detected on less than 1% of beef carcasses. About half of all beef consumed in the U.S. is in the form of ground beef. Any lot of raw ground beef in which E. coli O157:H7 is found will be recalled, and a press release will be issued warning consumers of the finding. Unfortunately, a test for this bacterium cannot be confirmed as positive for 4 days, which is the same as the average time from beginning of processing to retail sale of ground beef. The new policy on E. coli O157:H7 marks the first time that a bacterium or any other pathogen in a raw food product has been declared an adulterant, and a number of food producers have questioned the USDA s authority to set such a regulation without a period for comment. The USDA will collect only 5,000 samples each year from the 1,900 federally inspected plants and 100,000 retail outlets that grind beef routinely. According to FSIS, The program is not statistically designed, but is intended to stimulate industry actions to reduce the presence of E. coli O157:H7 in raw ground beef. Ideally, FSIS would like manufacturers to monitor the critical control points including microbial condition of raw meats, sanitation of processing equipment, and temperature control in the plant to assure the microbiological integrity of raw meat. HACCP The USDA is not alone in propounding the use of critical control points in food production and processing. In January, the U.S. Food and Drug Administration (FDA) proposed rules for a hazard analysis and critical control point (HACCP) system in the seafood industry. This was followed in August by the FDA s announcement that it is contemplating a move toward adopting HACCP procedures as the basis of the safety-assurance program for the nation s food supply. The agency has concluded that HACCP is a science based, systematic approach to preventing food safety problems by anticipating how such problems are most likely to occur and by installing effective measures to prevent them from occurring. HACCP covers the entire history of a food product, from growth through processing, distribution, preparation, and consumption. The major elements of the HACCP system are listed on page 5. The FDA s current system for food safety, developed more than 50 years ago, relies on visual inspection of food facilities and testing of the final product. The approach is designed to react to problems as they occur, not to prevent them. The FDA s proposals for HACCP would mark a wide-ranging change in the federal government s approach to food safety. The FDA cites these advantages to the proposed system: HACCP emphasizes prevention. HACCP permits more effective government oversight. HACCP appropriately puts the major responsibility for food safety on manufacturers, processors, and distributors. HACCP will assist food companies in competing in the world market. The fourth benefit of HACCP has no direct bearing on public health but will loom as a critical factor as HACCP increasingly becomes a worldwide standard for ensuring food safety. HACCP is expected to serve as the basis for harmonization of food safety regulations among nations. In October, the National Association of State Departments of Agriculture (NASDA) called on Congress to include HACCP provisions for meat and poultry in the 1995 Farm Bill. To assist in bringing HACCP on line, The development of new rapid test methods to detect pathogens... is essential, according to NASDA. Detecting foodborne pathogens Identification of microbiological pathogens by standard and rapid methods plays an important role in food-safety programs, including those based on the HACCP approach. Traditionally, end-product microbiological testing has been used in conjunction with surveillance of operations and equipment to certify the safety of processed food. In a HACCP design, end-product testing can help verify that the program is working as planned. Microbiological testing can also be conducted on food samples at harvest, during storage, at various 4

5 The principles of HACCP 1. Analyze hazards. This involves identifying the biological, chemical, or physical properties that may cause a food to be unsafe to eat and establishing measures to control these hazards. 2. Identify CCPs. CCPs are locations at which hazards can be prevented or reduced to acceptable levels. 3. Establish critical limits for preventive measures associated with each identified CCP. Critical limits should be set on such measures as temperature, time, physical dimensions, moisture level, and ph. 4. Establish procedures to monitor CCPs. When a critical limit cannot be monitored continuously, monitoring intervals should be frequent enough to ensure that the procedure for controlling the hazard is under control. 5. Establish corrective actions to be taken when a critical limit has been exceeded. Such actions must include plans for proper disposition of food produced during a deviation and for correcting the cause of the noncompliance. 6. Establish effective recordkeeping systems that document the HACCP system. The written HACCP plan should include lists of the hazards, CCPs, and critical limits, as well as the monitoring and recordkeeping procedures to be followed. 7. Establish procedures to verify that the HACCP system is working. This involves ensuring that the critical limits are adequate and that periodic revalidation occurs. Adapted from: Federal Register, August 4, 1994 stages of processing, in stores and markets, at ports of entry, and in food service establishments. Testing can indicate the possible presence of pathogens based on indicator microorganisms, detect pathogens directly, or identify toxins or other metabolites of pathogenic microorganisms. Indicator methods for bacteria include the standard plate count (SPC) and detection of coliforms. The SPC, the most widely used procedure for determining the number of live aerobic bacteria in food samples, relies on growing the microorganisms until they become visible as colony-forming units (cfu). Coliform bacteria can indicate fecal contamination, and their presence can suggest poor sanitation where the food was grown, processed, or sold. Whereas a negative finding for coliforms requires only 1 or 2 days, positive identification of specific coliform bacteria, such as E. coli, can only be made after 2 to 4 days. Standard tests for specific pathogenic bacteria can take several days. For Salmonella and Listeria, 4 days are required for a negative test, 7 days for a positive. A test to confirm the presence of toxin-producing Staphylococcus strains takes 4 days. Standard microbiological tests are useful for testing ingredients that go into processed foods and for end-testing. In some cases, the presence of toxins can be assumed if toxin-producing bacteria are detected. Toxins and metabolites are detected directly by a variety of laboratory methods, including radioimmunoassay, enzyme immunoassay, and enzyme-linked immunoabsorbent assay. Research into rapid tests for pathogenic microorganisms is a part of the FDA s food-safety program. Rapid tests will be needed for implementing HACCP procedures, especially the monitoring of critical control points along processing lines. Some rapid tests including ones for Listeria, Salmonella, and E. coli O157:H7 are already available as commercial kits. Rapid tests often depend on measuring a microorganism s metabolic products, such as toxins and organic acids. AOAC International, working with FSIS, will provide independent validation of kits sold commercially for detecting pathogens in meat and poultry. AOAC will not officially sanction the kits but will verify that they perform according to the manufacturers claims. As faster, more specific, and more sensitive tests for foodborne pathogens are developed, sophisticated statistical techniques can be applied to answering such questions as the actual number of cases of foodborne disease, the source of foodborne pathogens, and the numbers of cases caused by various pathogens. 5

6 How safe can our food be? New techniques for preserving food will play a role in controlling foodborne pathogens. Ionizing radiation, a method already approved in the U.S. for pork and poultry, can destroy all pathogenic and spoilage microorganisms in food products that have been processed, packaged, and sealed. If this technique is accepted by the public, it could render some foods, such as raw meats, pathogen-free at the time of their purchase. For the most part, however, the goal of food-safety programs cannot be the elimination of pathogenic microorganisms but the reduction of risks to acceptable levels. In addition to its interest in HACCP programs, the USDA is supporting legislation calling for the agency to establish levels of pathogens in meat and poultry that constitute a threat to human health. These levels will give due consideration to high-risk and immunocompromised populations. Improved methods of detecting and controlling microbiological pathogens, coupled with pragmatic new approaches to regulating food production, will make a wider variety of food available to consumers while continuing to reduce their risk from foodborne pathogens. References Council for Agricultural Science and Technology (CAST). Foodborne Pathogens: Risks and Consequences. Task Force Report No. 122, September Federal Register, Vol. 59, No. 149, August 4, 1994, pp Food Chemical News, October 24, 1994, pp , 47-48; October 17, 1994, pp. 13, 41-43; September 26, 1994, pp Notermans, S., G. Gallhoff, M.H. Zwietering, and G.C. Mead. The HACCP concept: Specification of criteria using quantitative risk assessment. Food Microbiology 11: , Notermans, S., M.H. Zwietering, and G.C. Mead. The HACCP concept: Identification of potentially hazardous micro-organisms. Food Microbiology 11: , Pierson, M.D., and D.A. Corlett, Jr. HACCP: Principles and Applications. Van Nostrand Reinhold, New York, About the author A bacteriology research assistant in the Nutritional Chemistry department, Kasey Herbst came to Hazleton earlier this year to reestablish the food bacteriology group. She holds a BS in bacteriology from the University of Wisconsin Madison. Previously, Kasey worked at Northland Food Laboratory, where she performed assays involved in the microbiological examination of foods and conducted analyses for Listeria, Salmonella, and E. coli by traditional and rapid methods. a Life Sciences Inc. Company ISO 9001 Registered The Hazleton Food Science Newsletter is published as a scientific information resource for the food and feed industries. Comments should be directed to: John Wolf, editor, PO Box 7545, Madison, WI Phone: (608) Fax: (608) Technical consultants: Randy Smith, Paul Kirkegaard, Darryl Sullivan, Joe Polywacz, Kevin Williams, Wayne Ellefson Hazleton Worldwide Locations Madison, Wisconsin (608) Vienna, Virginia (703) Harrogate, United Kingdom (44) Tokyo, Japan (81) Münster, Germany (49) Hazleton