A benchmark study into the potential connection between cattle production and antimicrobial resistance in humans shows no major link for most key antimicrobial resistance concerns.

"Many significant resistance concerns that we were looking for when we started this project turned out not to be an issue," says study leader Dr. Ronald Read of the University of Calgary, who unveiled findings at the recent National Beef Science Seminar in Calgary.

Most notably, vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA), of tremendous importance to human medicine, were not found in feedlot cattle, says Read, associate professor, Medicine and Microbiology & Infectious Diseases, University of Calgary, Faculty of Medicine.

"While it has been speculated that VRE in humans in Europe arose from feeding subtherapeutic levels of avoparcin to livestock, this practice was never used in cattle in Canada. There is no evidence that existing feedlot practices promote or select for either of these two resistant organisms," says Read. "Furthermore, Salmonella with multiple forms of resistance, reported to be found in outbreak situations in food animals, were not found in any of the feedlot animals we studied."

The multi-component study was funded in part by the Canada Alberta Beef Industry Development Fund (CABIDF), one of the country's largest beef research funds, which has funded over $16 million in research. The most comprehensive study of its kind, the research was conducted at four Calgary-area feedlots and in research-model feedlots in Lethbridge.

When this study began in 1999, scientists collected clinical samples from 2,622 feedlot calves upon arrival in the feedlot, during the feedlot period and before processing. The research team also collected clinical samples from 61 people working in the feedlots to measure whether those individuals acquired resistant organisms while working in the feedlot environment. Research scientists spent the past three years performing detailed susceptibility tests on the bacteria recovered, and analyzing the data.

Read, led a team of microbiologists and feedlot health specialists including Dr. Douglas Morck, and Dr. Kevin Laupland of the University of Calgary, along with Dr. Tim McAllister, Dr. Doug Inglis and Dr. Jay Yanke of Agriculture and Agri-Food Canada's Lethbridge Research Centre.

The study identified one form of resistance of potential concern for human medicine: a broad spectrum resistance to cephalosporins in some strains of cattle E. coli also resistant to ampicillin. "Ampicillin resistance itself is common among E. coli of both human and bovine origin," says Read. "There was no evidence to show direct transmission of AmpC-type E. coli from cattle to humans in our study." The authors recommend that cephalosporin resistance be monitored further.

Antimicrobial agents are the drugs, chemicals and other substances used in medicine to kill or slow the growth of microbes, particularly those that cause disease. When antimicrobial agents are over-used, studies show this can contribute to the build-up of resistance because it places added selection pressure on the microbe population to change in ways that allow it to survive an antimicrobial attack.

Resistance to antimicrobial agents used in human medicine has been on the rise worldwide in the past decade. While the widespread use of antimicrobial agents in human medicine is widely viewed as the primary factor contributing to this problem, the use of these agents in livestock production has also been speculatively linked as a contributing factor, although supportive data is sparse.

Through CABIDF, the Alberta beef industry funded the study by Read and colleagues to look for potential problems. CABIDF is a joint fund co-founded by Agriculture and Agri-Food Canada and Alberta Agriculture, Food and Rural Development. It was administered by Alberta Beef Producers.

More information. More detail on results of this study are available in this Research Report.

 Canada Alberta Beef Industry Development Fund