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U.S. Department of Health and Human Services

Animal & Veterinary

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Factors affecting numbers of acid-resistant Escherichia coli in cattle

Principal Investigator: Dr. James Russell
Organization: Agricultural Research Service, U.S. Department of Agriculture


In recent years, there has been a dramatic increase in food-borne illness, and Escherichia coli O157:H7 has proven to be a highly virulent pathogen. The virulence of E. coli O157:H7 has been explained by its toxin production, but this bacterium is also highly acid-resistant. The acid-resistance of E. coliallows it to survive the gastric stomach and colonize the intestinal tract of man. E. coli O157:H7 infection is often linked to contaminated beef, and cattle appear to be a natural reservoir. Improvements in sanitation can decrease the risk of E. coli O157:H7 at slaughter, but it is virtually impossible to prevent all fecal contamination. Preliminary findings indicate that grain feeding, a practice common in the American cattle industry, seems to increase the numbers of E. coli as well as its acid-resistance. Most of the beef cattle in the U.S. are also fed the ionophore, monensin, and preliminary experiments indicated that E. coli is very resistant to this antibiotic. The long term objectives of this proposal are to

  1. define the role of grain-feeding and feed additives in the dissemination of acid-resistant Escherichia coli from cattle, and
  2. find dietary strategies that could reduce the numbers of acid- resistant E. coli in cattle feces.

The specific aims of this proposal are to

  1. conduct cattle feeding trials to monitor the effect of grain and feed additives on the numbers of acid-resistant E. coli and define more precisely the colon pH and volatile fatty acid concentration that is needed to trigger the acid-resistance of E. coli in vivo,
  2. see if dietary dependent differences in E. coli acid-resistance will persist in raw hamburger,
  3. monitor the acid resistance, colicin production and genetic diversity of E. coli strains isolated from cattle fed different diets, and
  4. determine the effect of pH, volatile fatty acids, oxidation-reduction potential and nutrient starvation on E. coli O157:H7, an acid-resistant strain that causes food-borne illness. The proposed research has the potential of defining relatively simple dietary changes that could reduce carcass contamination and food-borne illness (withdrawal of monensin and the feeding of forage rather than grain in the period just before slaughter).