CHICAGO-The unusual and hardy characteristics of the pathogen Escherichia coli O157:H7 "have prompted food microbiologists to rewrite the rule book on food safety," according to the Institute of Food Technologists' (IFT's) October 1997 Scientific Status Summary "Foodborne Disease Significance of Escherichia coli O157:H7 and Other Enterohemorrhagic E. coli."
"E. coli O157:H7 is more significant than other well-recognized foodborne pathogens for reasons including the severe consequences of infection that affect all age groups, its low infectious dose, its unusual acid tolerance, and its apparent special but inexplicable association with ruminants [cattle, deer, and sheep] that are used for food," wrote Robert L. Buchanan, Ph.D., and Michael P. Doyle, Ph.D., the document's authors.
Less than ten E. coli O157:H7 cells may cause foodborne illness in people. Infectious doses associated with this pathogen in outbreaks have been consistently low?a characteristic associated with the organism's acid tolerance, according to Buchanan and Doyle.
Unlike most other pathogens, E. coli O157:H7 has been known to survive for several weeks to months in acidic foods such as fermented sausage and apple cider, and experimentally, in foods like mayonnaise and cheddar cheese. The survival time in these foods is greatly extended at refrigeration temperatures (32 F-40 F) as opposed to room temperature. Recent studies have also indicated that acid tolerance may increase the pathogen's resistance to other stresses such as heat, radiation, and antimicrobials.
"[E. coli O157:H7's] low infectious dose in combination with the disease severity means that successful prevention strategies must focus on reducing or eliminating the presence of the microorganism, rather than on preventing pathogen growth as is done in more traditional approaches," Buchanan and Doyle wrote.
The Hazard Analysis and Critical Control Point (HACCP) system can reduce the risk of E. coli O157:H7 infections, but it is not infallible, especially due to the pathogen's nature.
"For example, the low incidence of E. coli O157:H7 in foods makes direct microbiological testing for the pathogen as a means of verifying the effectiveness of a HACCP program of limited benefit," Doyle and Buchanan wrote. "Most desirable is a process that includes a step lethal to the pathogen." Current effective lethal steps include heat pasteurization for milk and juices and ionizing radiation for meat (if approved) and fresh fruits and vegetables.
Ionizing radiation is a promising technology because it can eliminate E. coli O157:H7 while maintaining the raw character of foods. Though approved for use with poultry, pork, and fresh produce in the United States to control various pathogens, this technology is extremely underutilized. Approval for its use with beef and seafood is pending.
The use of steam to briefly heat carcass surfaces to temperatures that will kill E. coli O157:H7 without cooking the meat is a new, promising food safety method. Steam pasteurization has been reported to achieve up to a 1000-fold reduction of E. coli O157:H7 on treated carcasses.
Beyond these processing measures, the only way to eliminate E. coli O157:H7 is by cooking ground beef and venison to at least 160 F at home and in foodservice kitchens. Unpasteurized juices, if consumed at all, should be also heated to 160 F.
Growers of produce should not fertilize plants with fresh manure. In an editorial accompanying IFT's Scientific Status Summary, I. Kaye Wachsmuth, Ph.D., wrote, "The tradition of recycling manure for vegetable gardening has caused E. coli O157:H7 illness; the pathogen can survive longer than the traditional 60-day holding period."
Though potentially deadly to humans, E. coli O157:H7 is not pathogenic to cattle. Despite this, the bacteria have the ability to persist in and reinfect cattle, even those that have a strong immune response to it, Buchanan and Doyle wrote. Results of two major U.S. surveys indicated that about 3 percent of dairy calves and 2 percent of feedlot cattle had E. coli O157:H7. Young animals tend to carry the pathogen more frequently than adults.
Though ground beef has been most often associated with E. coli O157:H7 outbreaks in the United States, other implicated foods include raw milk, apple cider, dry-cured salami, lettuce, produce from manure-fertilized gardens, potatoes, radish and alfalfa sprouts, yogurt, sandwiches, and water.
For a copy of IFT's Scientific Status Summary, contact Angela Dansby at (312) 782-8424 X134.
Robert L. Buchanan, Ph.D. is research microbiologist of the Food Safety Research Unit in the U.S. Department of Agriculture's Agricultural Research Service. Michael P. Doyle, Ph.D., is director of the Center for Food Safety and Quality Enhancement and head of the Department of Food Science and Technology at the University of Georgia. I. Kaye Wachsmuth, Ph.D., is deputy administrator of the Office of Public Health and Science, USDA Food Safety and Inspection Service.
FACTS ABOUT E. COLI O157:H7
- E. coli O157:H7 is one of the most virulent (highly infectious) pathogens known to enter the world food supply. It causes diarrhea, abdominal pain, and in some cases, intestinal bleeding and kidney failure.
- The initial symptoms of E. coli O157:H7 illness generally occur within two days after eating contaminated food, though three to five days have been reported. Symptoms increase in intensity during the next 24-48 hours, lasting from four to 10 days.
- Less than ten E. coli O157:H7 cells may be enough to cause foodborne illness in humans. A low infectious dose of two to 2,000 cells has been associated with outbreaks.
- E. coli O157:H7 can survive in acidic environments that are lethal to other pathogens, such as in fermented foods like sausage and apple cider.
- Though potentially deadly to humans, E. coli O157:H7 is not pathogenic to cattle.
- A single cow, or cattle within the same herd, may contain more than one strain of E. coli O157:H7. Some strains are thought to have greater acid tolerance than others.
- The source of E. coli O157:H7 contamination on carcasses is likely due to fecal contamination during animal production and slaughter operations. Carcasses may become contaminated during hide removal or by cross-contamination with equipment and workers' hands.
- HACCP systems in processing plants cannot eliminate E. coli O157:H7 from foods unless a treatment is added that will kill the pathogen, such as heat pasteurization or irradiation.
- Current research shows that competitive exclusion has the potential to eliminate E. coli O157:H7 from cattle before slaughtering. Competitive exclusion involves the use of non-pathogenic microorganisms to outgrow pathogens in the gastrointestinal tracts of animals.
- If swallowed, fecally contaminated water in freshwater swimming areas may cause E. coli O157:H7 infection in both cattle and humans.
- Fresh manure used to fertilize garden fruits and vegetables may contaminate them with E. coli O157:H7.
- The largest reported E. coli O157:H7 outbreak, which caused thousands of illnesses, occurred in Japan in 1996. Radish sprouts were implicated as the source of infection.
CONSUMER FOOD SAFETY TIPS
- Wash hands well before handling food and after handling raw meat or poultry, petting animals (especially cattle, deer, or dogs), changing diapers, providing day care to children or adults, etc.
- Wash fruits and vegetables thoroughly prior to handling or eating.
- Do not use fresh manure to fertilize garden fruits or vegetables.
- Drink only pasteurized milk and apple juice.
- Cook ground beef, venison, poultry, and pork thoroughly (minimum 160 F) before eating.
- Avoid cross-contaminating food with raw meat or poultry.
- Avoid swimming in lakes or ponds used by cattle.
- Avoid drinking surface water that has not been treated to eliminate pathogens.