A disturbing worldwide trend over the past decade has been the emergence of microbe populations resistant to antimicrobial agents used in veterinary and human medicine.

“It's a very serious issue,” says Ron Read, associate professor, Medicine and Microbiology and Infectious Diseases, University of Calgary. “Obviously, as more agents are rendered less effective due to increased populations of antimicrobial resistant microbes, humans and animals that depend on those agents to battle disease become more vulnerable.”

Use of antimicrobial drugs in cattle production, however, isn't a major contributor to the development of resistant bacteria that threaten human health. That's according to a five-year study of antimicrobial resistance in Alberta feedlot cattle by the University of Calgary and Agriculture and Agri-Food Canada.

“The most significant resistance concerns that we went looking for, turned out not to be an issue,” Read says. Most notably, bacteria with resistance to vancomycin and methicillin, the top human health concerns speculatively linked to cattle production, were not found in Alberta feedlot cattle. Salmonella, with multiple forms of resistance, widely thought to be in outbreak situations in food animals, were also not found.

Only one form of resistance of potential concern for human medicine was found — E. coli strains with resistance to cephalosporins. However, prevalence of this resistance in humans is extremely low and researchers consider the potential for relevant transfer from cattle to humans unlikely.

“We're in a situation where we've identified something that needs to be monitored,” Read adds. “We're fortunate we have time to keep an eye on this situation and deal with it.”

Read makes the following points:

  • The more widely and frequently an antimicrobial is used, the greater the risk of antimicrobial resistance.

  • Antimicrobial resistance that threatens human health is primarily associated with antimicrobial use in human medicine and the role of hospitals as reservoirs of resistant organisms. However, there's been widespread concern antimicrobial use in livestock production is also a contributing factor, with resistant microbes transferred to humans through direct contact, the environment and food products.

The new study was the most comprehensive of its kind and the first to examine Canadian cattle. The cephalosporin resistance was a surprise finding and its significance is unknown.

“The most important thing is to continue to keep an eye on this phenomenon,” Read explains. Health Canada is establishing a surveillance system for antimicrobial-resistant organisms in agriculture.

Read and his colleagues have proposed that resistant microbes identified in their study be included in this monitoring program. Production management changes may also be warranted, he says.

More on the study and Read's views are available in a new article on the Meristem Land and Science Web site, www.meristem.com.