Objective—To describe geographic, farm-type, and animal-type factors associated with multiple antimicrobial resistance (MAR) in fecal Escherichia coli isolates from cattle.
Design—Cross-sectional field study.
Sample Population—1,736 fecal samples from cattle on 38 farms in California, Oregon, and Washington.
Procedures—Fecal samples were collected from preweaned calves (2 to 4 weeks old) and cows that recently calved on dairy and beef cow-calf farms, preweaned calves on calf ranches, and 1-year-old steers on feedlots. One fecal E coli isolate per sample was isolated, and antimicrobial susceptibility was tested. Escherichia coli isolates were initially clustered by antimicrobial resistance patterns and categorized by number of antimicrobial resistances. A generalized estimating equations cumulative logistic regression model was used to identify factors associated with an increase in MAR in fecal E coli isolates from cattle.
Results—MAR was higher in E coli isolates from cattle in California, compared with those from cattle in Washington or Oregon. Multiple antimicrobial resistance was highest in E coli isolates from calves on calf ranches and progressively lower in isolates from feedlot steers, dairy cattle, and beef cattle. Multiple antimicrobial resistance was higher in E coli isolates from calves than from adult cattle, in E coli isolates from cattle of conventional farms than of organic farms, and in isolates from beef cattle in intensive dairy farm regions than from beef cattle distant from dairy farm regions.
Conclusions and Clinical Relevance—MAR in fecal E coli isolates from cattle was influenced by factors not directly associated with the use of antimicrobials, including geographic region, animal age, and purpose (beef vs dairy).