Vet Column 6-28-10 | TheFencePost.com

Vet Column 6-28-10

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

Antimicrobials are critical tools in promoting both animal and human health. Because animals, humans and the potential microbes that are associated with disease and those that do not cause disease are all biological organisms, dynamic processes for survival of each occur continuously. Potential misuse of antimicrobials by both human patients and their caregivers, and animal health caregivers remains an important issue within the public health and animal health arenas.

Authors from the University of California-Davis and Washington State University have recently published data investigating multiple antimicrobial resistance in fecal E. coli isolates from cattle in the western United States. This publication reinforces the complexity of the issue and the answers are not black and white. It does, however, present some interesting findings.

Previously reported studies in cattle have shown that farm type, animal age category, antimicrobial treatment, management and other factors influence the degree and pattern of antimicrobial resistance in fecal E. coli. Data from multiple studies indicate that multiple antimicrobial resistance cannot be solely attributed to antimicrobial exposure alone. This recently reported study was intended to describe geographic, farm type and animal type factors associated with multiple antimicrobial resistance in fecal E. coli on dairy farms, feedlots, calf ranches and beef cow-calf operations in California, Oregon and Washington.

Fecal samples were obtained from 1,736 cattle on 38 farms in California, Oregon and Washington. Animal types included preweaned calves (2-4 weeks-of-age); cows that recently calved on dairy and beef cow-calf farms; preweaned calves on calf ranches; and 1-year-old steers on feedlots. Dairy farm types included organic and conventional. Beef cow-calf operations included those within one mile of a dairy and those more than 20 miles from a dairy. One fecal E. coli isolate per samples was isolated, and antimicrobial susceptibility was tested. Twelve different antibiotics were assayed for resistance patterns.

Results from this study indicate that multiple antimicrobial resistance 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 was 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.

Although not part of this study, Canadian data indicates that the degree of antimicrobial resistance was not associated with breed of cow and breed or sex of calf.

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Most importantly, this study demonstrates that multiple antimicrobial resistance in fecal E. coli isolates from cattle was influenced by factors not directly associated with the use of antimicrobials and further supports data from multiple other studies. Factors such a geographic region, animal age and purpose such as dairy or beef can affect multiple antimicrobial resistance.

Just because antimicrobial resistance is not due to antimicrobial use alone, however, inappropriate use of antimicrobials in animals cannot be condoned. The complex issue of antimicrobial resistance is not going away nor should it. All animal health caregivers should follow label and prescription directions when using antimicrobials for animal treatment. It’s also a good idea when working with your physician.