PULLMAN, WA/USA, June 28th (Biermann) – In a cross-sectional field study performed by American researchers under the lead of Dr. Thomas E. Besser from the Department of Veterinary Microbiology and Pathology of the College of Veterinary Medicine at the Washington State University in Pullman (Washington), researchers tried to determine factors that contribute to the increasing antimicrobial resistance of E. coli in cattle.

They analyzed a total of 1736 fecal samples from cattle of 38 farms that reside in California, Oregon and Washington. The cattle considered for the study were either preweaned calves (two to four weeks of age) and cows that recently calved on dairy and beef cow-calf farms, preweaned calves on calf ranches and one-year-old steers on feedlots. The authors write that they isolated one fecal E. coli type per sample and submitted it to antimicrobial susceptibility testing. The results were collected and sorted according to resistance patterns and by number of antimicrobial resistances. They then used a generalized estimating equations cumulative logistic regression model to calculate factors that were associated with multiple antimicrobial resistance (MAR) in fecal E. coli isolates from cattle.

They noticed a higher MAR prevalence among E. coli isolates from cattle in California, in comparison to cattle from Washington or Oregon. The highest MAR was detected in isolates from calves on calf ranches. In feedlot steers, dairy cattle, and beef cattle the resistance became progressively lower. Generally speaking, Dr. Besser and his associates noticed higher MAR in calves than in adult cattle, in cattle from conventional farms than from organic farms, and in beef cattle from intensive dairy farm regions than from beef cattle distant from dairy farm regions.

Thus, antimicrobial resistance seems not only to be influenced by factors directly associated with the use of antimicrobials. The geographic region (dairy farm region vs. non-dairy farm region), animal age (calf vs. adult animal) and purpose (beef vs. dairy) plays an important role as well, the authors conclude in their report that appeared in the July issue of Journal of the American Veterinary Medical Association.

References

• JAVMA 236(12):1338-1344