On-farm E. coli O157:H7 Control?
Editor’s note: Following the recent release of the Independent Review of XL Foods Inc. Beef Recall 2012, we thought it timely to pull this article from the archives to help address any questions about pre-harvest interventions or on-farm practices to mitigate food safety risks. See below for links to more science-based information on E. coli O157:H7 and summaries of industry-funded research which strives to find practical, economical and effective solutions to reduce or prevent pathogen contamination throughout the production chain. Stay tuned to the BCRC Blog to learn about upcoming food safety research funded within the Beef Cattle Industry Science Cluster under Growing Forward 2.
This article written by Dr. Reynold Bergen, BCRC Science Director, originally appeared in the November 2012 issue of Canadian Cattlemen magazine and is reprinted with permission.
E. coli O157:H7 has raised its ugly head again with the unfortunate illnesses and massive cross-Canada beef recall. E. coli bacteria are naturally found in the digestive tract of all warm-blooded animals. There are many strains of E. coli. Most strains are harmless and some may have health benefits. But E. coli strains that produce Shiga toxins can be very dangerous. When humans absorb Shiga toxins they can experience severe abdominal cramps and bloody diarrhea. Recovery can take over a week. Consequences can be more severe or even fatal in patients who are very young, very old, or have weak immune systems. E. coli O157:H7 does not cause illness in cattle because cattle do not have receptors for Shiga toxins.
Packing plants have implemented very effective interventions to reduce that E. coli O157:H7 from the hide or gut contents will contaminate beef. However, recalls sometimes raise questions about whether on-farm practices may have prevented the problem. This article summarizes some on-farm E. coli O157:H7 control approaches that have been tested.
Replacing grain with forage: This approach is based on the theory that E. coli O157:H7 may be more acid-tolerant than other microbes. When high-starch (grain) diets are fed, some starch escapes fermentation in the rumen and is fermented by microbes in the hind-gut. The fermentation produces volatile fatty acids that make the hindgut more acidic. Acid-tolerant microbes like E. coli O157:H7 may survive, compete and proliferate better than other microbes in that environment. Because forages have less starch, less acid is produced when they are digested, and E. coli O157:H7 might be less likely to proliferate. However, forage feeding doesn’t consistently reduce E. coli O157:H7. A 2009 article by Dr. Megan Jacob, Todd Callaway and T.G. Nagaraja in “Foodborne Pathogens and Disease” reviewed 10 studies that compared E. coli O157:H7 in animals fed forage-based and grain-based diets. Three studies showed that E. coli O157:H7 shedding was increased in forage-based diets. Four showed no difference. The other three observed higher rates of E. coli shedding in grain-fed cattle, but E. coli O157:H7 numbers were not specifically reported.
Direct-fed microbials (probiotics): Some bacteria (particularly Lactobacillus and Propionibacterium) may be able to outcompete and inhibit E. coli O157:H7 in the digestive tract of cattle. Some trials have shown encouraging results, but a trial conducted by researchers from Agriculture and Agri-Food Canada, Alberta Agriculture and Rural Development (ARD) and Feedlot Health Management Services found that a direct-fed microbial containing Lactobacillus and a yeast did not reduce E. coli O157:H7 prevalence on the hide or in feces. This variability may be because it is difficult to ensure that each animal consumes the right amount of probiotic every day.
Vaccines: A made-in Canada vaccine is licensed as an aid to reduce E. coli O157:H7 shedding when three doses are given, three weeks apart, followed by a 60 day withdrawal period. Effects on shedding have varied among trials, and the vaccine does not have a food safety claim. A competing US vaccine is not registered in Canada.
Other approaches (like phages, seaweed supplements, and antibiotics) have also shown inconsistent results. Some reduce the numbers of bacteria shed, or the duration of shedding, but none of them completely eliminate E. coli O157:H7. None of these approaches work consistently in all animals, so E. coli O157:H7 can still be spread to other herd mates. It is not known whether these strategies will reduce the E. coli O157:H7 load in live cattle enough to make the in-plant food safety interventions more effective. Very little research has been done in this regard.
Interventions not only need to work, they also need to be used. The challenges facing on-farm E. coli O157:H7 interventions are similar to those that have stymied genetic improvement or preconditioning programs. The cattle production and marketing system is so complex it is often impossible to know whether a pre-harvest E. coli intervention has been used (or used correctly) by a previous owner.
Another complication comes from the fact that E. coli O157:H7 is not the only harmful serotype of E. coli; there are at least six others (O26, O45, O103, O111, O121, and O145). Interventions specific for E. coli O157:H7 may not provide cross-protection to any or all of these other six strains.
A number of other potential foodborne pathogens are occasionally found in cattle, including Campylobacter, Enterococcus, Listeria, and Salmonella. Effective food safety interventions will prevent any of these pathogens from moving from the hide or gut contents onto the carcass, and eliminate any pathogens that do contact the beef. At present, the packing plant is the best place to effectively combat the full range of foodborne pathogens. Efforts to improve on-farm interventions will continue, but may not replace food safety measures implemented at packing plants.
BeefResearch.ca >> Food Safety
Includes fact sheets on BCRC-funded E.coli research.
E.coli O157:H7: an Industry Research Priority
BCRC Blog – October 5, 2012
A summary of producer level, processing level and environmental industry-funded research related to E.coli O157:H7.
How do carcass processing procedures impact food safety?
BCRC Blog – May 24, 2013
E-beam irradiation research: new fact and video
BCRC Blog – May 21, 2013
BCRC Blog – April 29, 2013
Food Safety Research on Mechanically Tenderized Beef
BCRC Blog – February 11, 2013
On-farm Practices to Improve Food Safety
BeefResearch.ca >> Food Safety
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