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Research   »   E. coli

E. coli

E. coli (short for Escherichia coli) is a species of bacteria naturally occurring in digestive tracts and are needed to keep animals healthy. There are hundreds of different strains. Most strains are beneficial or harmless to animals, including humans. A few strains can be dangerous to people, but as many of the same control measures work for all dangerous E. coli, only the strain that causes the most human disease will be discussed.  E. coli O157:H7 is a major dangerous strain and is shed in the manure of many warm-blooded animals, including deer, geese, dogs and cattle. E. coli O157:H7 is harmless to most animals but is dangerous to humans, especially to those with an immature or weakened immune system, because it produces a toxin that can cause severe illness. People can become infected by consuming undercooked meats, fruits, vegetables or water that was contaminated by E. coli O157:H7. Cow-calf producers, feedlots, transporters, processors, retailers and consumers all play an important role in reducing or eliminating incidences of E. coli O157:H7.

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Key Points

  • There are many strains of E. coli; most are harmless to animals including humans. E. coli O157:H7 is a major dangerous strain to humans and is shed in the manure of many warm-blooded animals including cattle.
  • Producers, processors, retailers and consumers all play an important role in reducing or eliminating incidence of E. coli O157:H7.
  • Research works to find practical, economical and effective solutions to reduce or prevent E. coli O157:H7 throughout the production chain.
  • Cattle producers should assume that E. coli O157:H7 is present in their herd. Ensuring pens and transport trailers have adequate, clean bedding, that water from cattle pens does not flow into or near surface water or wells, and that animals shipped to processors have little or no tag may minimize contamination.
  • A vaccine for cattle was developed in Canada to aid in the reduction of E. coli O157:H7 shedding, but is not currently available. Designing a vaccine that consistently controls shedding in live cattle is difficult as E. coli O157:H7 does not cause disease in cattle.
  • Methods used by Canadian processors are proven very effective in reducing the pathogen load in meat, and contamination is extremely rare.
  • All ground beef products (including those from a “source grind”) such as hamburgers and sausages or mechanically tenderized steaks must be cooked to an internal temperature of 160oF or 71oC, which will kill the bacteria if present.

Human Exposure to E.coli O157:H7

E. coli 0157:H7 is a resilient bacterium that is very common in the environment. It can survive and replicate in a wide range of conditions, including with or without the presence of oxygen, and despite changes in pH and temperature. There are four major routes of human exposure:

E. coli O157:H7 is naturally occurring in many animals. It is not harmful to cattle, but can cause illness in humans.
  • Consuming undercooked meats that were contaminated at slaughter or during processing or preparation
  • Consuming fresh fruits and vegetables irrigated or washed with contaminated water
  • Exposure at fairs in which livestock are present, or at petting zoos
  • Consuming water from contaminated water sources, such as lakes, rivers, ponds, swimming pools, or wells that are not properly maintained or where water quality regulations are not enforced

Impact on the Canadian Beef Industry

Because cattle, like most other animals, shed E. coli O157:H7 through feces, and beef can become contaminated from hides and equipment during slaughter and processing, the entire industry takes steps to prevent incidences of contamination. This requires substantial investments in research, infrastructure and production practices.

“Shedding” - the excretion of a pathogen from the body.

Product recalls, triggered by suspected contamination of E. coli O157:H7, can cost the industry millions of dollars. Recalls are typically very extensive. The identification of a single positive result causes an entire batch of product to be recalled. These recalls are expensive to packers, processors and retailers and costs are inevitably passed on to producers. In addition to direct costs, analysts recognize that any food safety incident, whether real or perceived, that cause concern in consumers result in reduced prices and lost sales for 3-6 months or longer.

Research works to find practical, economical and effective solutions that can be implemented to reduce or prevent E. coli O157:H7 and other pathogen contamination throughout the production chain.

Producers' Role

Generally, if you look for E. coli O157:H7 in cattle across Canada, you are likely to find it. In one study, prevalence of E. coli O157:H7 in Saskatchewan feedlots ranged from 0% to 57.5% (Vidovoc and Korber, 2006). The majority of beef calves (87.5%) were found to have the O157 antigen prior to weaning, suggesting that they have been exposed to the pathogen at least as a calf (Laegreid and Keen, 2004). Therefore, it is recommended that producers assume that E. coli O157:H7 is present in their herds.

Reducing the spread of E. coli O157:H7 at the cow-calf and feedlot levels is important, yet very difficult to effectively manage. Continued research to discover on-farm strategies that consistently decrease E. coli O157:H7 in live cattle is identified as a high priority for the industry. The relationship between decreased shedding of E. coli O157:H7 by live animals and food safety is difficult to measure and therefore unclear.

Much research has been done to understand E. coli O157:H7 in cattle in feedlot settings. This is because feedlots are the last home for most cattle before slaughter, and because cattle are grouped in feedlots, making data easier to gather.

Through numerous feedlot studies, the origin and behaviour of E. coli O157:H7 in feedlots is well known, including:

  • Cattle with E. coli O157:H7 in their digestive tract show no clinical signs.
  • E. coli O157:H7 is found in cattle populations across the country, in every environment.
  • Seasonal differences in shedding have been noted. Shedding peaks in summer and early fall.
  • Age and stress affects shedding and it is highest in newly weaned calves
  • Most shedding by cattle is temporary, lasting approximately 4 weeks, and the numbers of E. coli O157:H7 shed by cattle can vary widely, even within one day.
  • Cattle can have multiple bouts of shedding as there may not be a strong enough immune response to prevent subsequent shedding.

Basic Husbandry

Ensuring pens have adequate, clean bedding with proper water drainage will minimize the potential for pathogens. Shipping animals to the packer that are clean, with little or no tag (clumps of mud and manure on the hide), may minimize contamination of the carcass at the processor level. Transport trailers should be cleaned and adequately bedded before animals are loaded.

Unfortunately, research has shown that regular pen cleaning and frequent, aggressive cleaning of water troughs does not have any effect on rates of E. coli O157:H7.

Cattle Diets

Although E. coli O157:H7 has been found in feed, no association between presence in feed and the pathogen’s prevalence in live animals has been found.  No clear association has been found between feed ingredients and shedding of E. coli O157:H7 by cattle.


A vaccine for cattle was developed to aid in the reduction of E. coli O157:H7 shedding in cattle. The vaccine is licensed for use in Canada, but is currently not available. The BCRC contributed to funding early research for the vaccine.

Water protection

Cow-calf producers and feedlots should manage their water drainage from cattle pens to ensure the water does not directly flow into surface streams and creeks, or areas close to lakes or wells.

Irrigation canals and sensitive riparian areas along streams and rivers should be fenced or lined with buffer strips to reduce the access of cattle to the water. Completely limiting the access of cattle to surface water on grazing lands is impractical and wild ruminants (deer, moose) aquatic mammals (beavers, musk rats) and birds (geese, ducks) that occupy the ecosystem can also carry the bacteria.

Untreated water drained directly from livestock operations should not be used to irrigate fruit or vegetable crops that are not cooked prior to consumption.

Processor Responsibility

Food safety is paramount to packers, and they invest heavily in methods to mitigate pathogens including E. coli O157:H7. Current practices in abattoirs and processing facilities include numerous and diverse methods, which vary slightly across facilities. Packers diligently ensure their practices comply with, if not exceed standards under hazard analysis critical control point (HACCP) plans. The methods used by processors are proven to be very effective in reducing the pathogen load in meat, and contamination is extremely rare.  New pathogen mitigation methods are being assessed as packers continually seek to improve the safety of their products.

Hide wash

Once the animal has been killed, it moves through a high-pressure, hot water rinse (hotter than 70oC)to kill pathogens on the hide before the hide is removed.

Careful dressing procedures

Workers take care to ensure that the hair side of the hide does not contact the carcass during hide removal. Careful evisceration ensures that the digestive tract is not perforated, so that gut contents do not contact the carcass surface.

Vacuum steaming

Once the hide is removed a steam vacuum is used to remove bacteria and visible fecal contamination by delivering continuous steam at 7 to 10 psi at 88-94oC while simultaneously vacuuming the area. The equipment is continually sanitized while in use.

Carcass trimming

Any visible contamination on a carcass is removed using knives and discarded.

Carcass washes

Once any visibly contaminated spots have been removed, carcasses move through washes. These washes may contain naturally occurring organic acids, such as lactic acid, to kill pathogens. 

Steam Pasteurization

Carcasses also pass through high temperature steam cabinet to pasteurize the surface.  After steam pasteurization, research studies have shown that E. coli O157:H7 becomes very difficult to detect on the surface of the carcass. 


Carcasses are aged in coolers at temperatures that prevent pathogen growth.


Workers clean gloves, knives and other equipment frequently to maintain hygiene, and tools, equipment and facilities are thoroughly cleaned between shifts.


After a detailed review of the scientific data that began in 2001, Health Canada concluded that irradiation for ground beef is safe, effective, and does not significantly impact nutritional quality when used in accordance with Canadian requirements. The Government of Canada approved the use of irradiation for both fresh and frozen raw ground beef on Feb 22, 2017. Irradiated ground beef has been available for sale in the USA since 2000.

Learn more about irradiation in this 2013 video:

Retail, Foodservice, and Consumer Responsibility

Safe food-handling

It is unknown how many E. coli O157:H7 organisms are required to cause illness, but it may be as low as ten.   Proper food handling, transport, storage, retail display and preparation will prevent the growth of pathogens and cross contamination with other foods and work surfaces. It is important that these safe food-handling guidelines are followed:

  • Keep meat refrigerated or frozen. Thaw in the refrigerator.
  • Keep raw meats and the cutting boards and utensils used to prepare them separate from other foods
  • Avoid cross-contamination by thoroughly washing work surfaces, equipment, utensils and hands after touching raw meats
  • Cook ground beef to an internal temperature of 160oF or 71oC
  • Keep foods hot before consuming
  • Refrigerate leftovers immediately

Cook to appropriate temperatures

E. coli O157:H7 can contaminate the surface area of beef during slaughter. The bacteria will only be found on the surface, not down within the muscle fibers. However, if contaminated meat is cut or ground, the bacteria can be carried down into the meat, or mixed throughout ground meat. Therefore, ground products, such as hamburgers or sausage, must be cooked to an internal temperature of 160oF or 71oC, which will kill the bacteria. A meat thermometer should be used to ensure internal temperatures have been reached before consuming. 


Vidovoc S, Korber DR. Prevalence of Escherichia coli O157 in Saskatchewan Cattle: Characterization of Isolates by Using Random Amplified Polymorphic DNA PCR, Antibiotic Resistance Profiles, and Pathogenicity Determinants. Appl Environ Microbiol. 2006 June; 72(6): 4347–4355.

Laegreid WW, Keen JE. Estimation of the basic reproduction ratio (R0) for Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) in beef calves. Epidemiol Infect. 2004 April; 132(2): 291–295.


Feedback and questions on the content of this page are welcome. Please e-mail us at info [at] beefresearch [dot] ca.


Thanks to Kim Stanford, Beef Scientist, Alberta Agriculture and Forestry, for contributing her time and expertise in the writing of this page.

This topic was last revised on June 6, 2019 at 11:06 AM.

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