E. coli O157:H7, the cause for the recent, extensive beef recall, is one of the few types of E. coli that is dangerous to humans. It is shed in the feces of many warm-blooded animals, including deer, geese, dogs and cattle. E. coli O157:H7 is harmless to most animals but can be dangerous to humans if contaminated water or undercooked meat is consumed, especially to those with an immature or weakened immune system. Beef can become contaminated by cattle hides and equipment during slaughter and processing or by food handlers in the retail sector.
Much research has been done to understand E. coli O157:H7 in cattle in feedlot settings, the last home for most cattle before slaughter, and where grouped cattle provide easier data collection. 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.
- Most infections in cattle are temporary, lasting approximately 4 weeks, and the numbers of E. coli O157:H7 shed by infected cattle can vary widely, even within one day.
- Infections come and go within animals. An infection may not produce a strong enough immune response to prevent subsequent infections.
- The rate of infection within feedlot pens varies between 0% – 57.5%, based on a study of feedlots in Saskatchewan.
Improved food safety continues to be a top research priority in the Canadian beef industry. Recent and ongoing research funded by the Beef Cattle Research Council (BCRC) strives to find practical, economical and effective solutions to reduce or prevent E. coli O157:H7 contamination throughout the production chain.
Producer level research
Continued research to discover on-farm strategies that consistently decrease E. coli O157:H7 in live cattle is a priority for the industry, however the relationship between decreased shedding of E. coli O157:H7 in live animals and food safety is unclear.
A study led by Dr. Kim Stanford (Alberta Agriculture and Rural Development) and Dr. Tim McAllister (Agriculture and Agri-Food Canada Lethbridge Research Centre) looked at whether feeding distillers’ grains to feedlot cattle increased the excretion of E. coli 0157:H7. Past research by U.S. researchers found conflicting results as to whether feedlot diets containing dried distillers’ grains with solubles (DDGS) increased the risk of E. coli shedding. The Alberta study provided more information on E. coli shedding in Western Canadian conditions, where most finishing diets are based on barley rather than corn, and where both wheat DDGS and corn DDGS are available. Results indicated that finishing diets containing 0% or 22.5% of DDGS did not affect the numbers of E. coli O157:H7 shed in manure. Shedding varied and declined over the course of the feeding period, which confirmed that many factors other than diet influence the risk of shedding.
The BCRC also funded some of the early research that led to the development of a vaccine that aids in the reduction of E. coli O157:H7 shedding in cattle. The vaccine is licensed for use in Canada, requiring three doses and a 60 day withdrawal period before slaughter. It typically costs $3 per dose. The vaccine has been shown to reduce shedding, but reduced shedding in live animals may not sufficiently reduce E. coli O157:H7 contamination on meat products. There is no evidence that immunization against E. coli O157:H7 with the current vaccine will provide any cross protection against the other potentially hazardous pathogens, such as Campylobacter, Listeria, Salmonella, or non-O157 STEC strains of E. coli. It is also well known that not all cattle respond equally to a vaccination program.
Using bacteriophages to reduce E. coli O157:H7 shedding in live animals has also been explored. Phages are viruses that attack bacteria. In the project, ‘Use of Bacteriophage to Control E. coli O157:H7 in Beef Cattle and the Environment’, three phages known to infect E. coli bacteria were tested. One of the phages destroyed 92-97% of the bacteria, while the other two destroyed 33-38% or fewer. However, the phages did not perform well in highly acidic conditions, like those in the stomachs of cattle. In a trial where multiple doses of the most effective phage were administered both before and after dosing live sheep with E. coli O157:H7, the phage was successful in reducing shedding of the bacteria. Further research on practical application is needed before this technology can be used in cattle production.
Processor level research
E. coli O157:H7 is more of a concern in beef trim and ground beef than in whole muscle cuts. On muscles, the bacteria are restricted to the outer surface, where it is relatively easy to combat. When beef trim is ground into hamburger, much more surface area is available for the bacteria to grow on. Consequently, much of the processor level research is focused on combatting the pathogen in beef trim.
Irradiation of beef can be very effective at eliminating food pathogens. Irradiation is approved for use on beef in the U.S., but not in Canada. Research led by Dr. Richard Holley of the University of Manitoba is currently underway, studying the use of e-Beam treatment to reduce the viability of E. coli O157:H7, non-O157 E. coli, and Salmonella on meat surfaces.
A two-part project led by Colin Gill, Ph.D. at the Agriculture and Agri-Food Canada Lacombe Research Centre is currently studying the effects of antimicrobial sprays, including lactic acid, on beef trim. The project will also do a cost:benefit analysis, comparing antimicrobial sprays, irradiation and trim pasteurization methods of combating pathogens. The results of the study, expected in Spring 2013, will be used to make recommendations to the Canadian beef industry on combating E. coli, Salmonella and Listeria, while maintaining appearance, shelf-life and eating quality.
To examine how E. coli O157:H7 survives in soil and to determine whether spreading manure as a fertilizer poses a risk for groundwater contamination, a study led by Darren Korber, Ph.D. at the University of Saskatchewan was conducted in 2004. The results found that soil is effective at filtering the bacteria. When infected manure was applied to soil, less than 10% of the bacteria was recoverable, and it did not migrate more than 50 centimeters.
Cow-calf producers, feedlots, transporters, processors, retailers and consumers all play an important role in reducing or eliminating incidences of E. coli O157:H7. Research and innovation provides greater understanding of E. coli shedding to inform management practices of live animals, and can lead to the development of practical technologies and procedures that simultaneously combat a variety of different pathogens to ensure food safety of beef products.
For more information on E. coli O157:H7 and the research projects mentioned in this article, visit the E. coli O157:H7 page at BeefResearch.ca.
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