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Antimicrobial myths and facts

Drug-resistant bacteria a “wicked problem.” Get to know the facts on this file

Antimicrobial resistance is a “wicked problem,” says Dr. John Campbell, requiring cooperation from many stakeholders.

The livestock industry’s contribution to antimicrobial resistance is hard to pin down, but hospitals and care centres for seniors are a much more common source of resistance, Campbell said during the Canadian Farm Writers’ Federation conference in Saskatoon in October. Campbell heads Large Animal Clinic Sciences at the Western College of Veterinary Medicine. His research focuses on disease surveillance and infectious diseases in beef cattle.

Campbell spent the better part of an hour going through antimicrobial resistance myths and facts. Antimicrobials are drugs used to treat infections caused by everything from bacteria to fungi. It’s a broader term than the more commonly used antibiotic, which refers to drugs that kill bacteria.

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About 75 to 80 per cent of antibiotics in Canada are used for livestock, Campbell said. But there are about 650 million livestock slaughtered annually in Canada. Measured by dose per patient (human or animal), people use more antibiotics than livestock.

Health Canada classifies antimicrobials by their importance to human health; low (Category 4), medium (Category 3), high (Category 2), and very high (Category 1). Most antimicrobials used in feedlots fall into Category 4, which aren’t used in human medicine. Less than one per cent of antimicrobials used in feedlots fall into Category 1 or 2, Campbell said.

“I think it’s pretty unlikely that resistant bacteria we might create in the animal agriculture are going to end up in the surgery unit. We’re probably dealing more with resistant bacteria in the gut caused by campylobacter and things like that,” Campbell said.

Any antimicrobial-resistant bacteria that evolve in the feedlot must escape food safety checks, and survive cooking, to make someone sick, he added. The odds of getting sick from drug-resistant campylobacter are about one in 236 million in the U.S., Campbell said.

But the agriculture industry does need to pitch in to prevent antimicrobial resistance, Campbell said. Canada has a “robust” antimicrobial resistance surveillance system, and much of the funding and drive for that system has come from the livestock industry, he said, but more needs to be done.

Research is ongoing. Campbell said a new beef cattle research facility is slated for construction outside of Saskatoon. Researchers will be doing a long-term environmental study on effluent and microbial waste at the new facility. Campbell hopes to also see antimicrobial resistance research as well.

Antibiotic residue or resistance?

Campbell is concerned that the general public doesn’t know the difference between antibiotic resistance and residue.

“All of our meat is almost guaranteed antibiotic-free. We have about a 99.7 per cent pass rate on residue issues. And many of those residue issues are caught in the plant.”

Maximum residue limits are a “caution sign,” Campbell said. “They’re not really a danger sign. There’s huge safety margins built in.”

For example, the acceptable daily intake of tetracycline in humans is 30 micrograms per kilogram of body weight. The maximum residue limit for beef is about 200 micrograms per kilogram. If someone served Campbell beef that was at that maximum residue limit, he could eat three 74 gram servings per day, and he’d still only consume two per cent of his acceptable daily intake. Campbell adds beef usually has negligible or no antimicrobial residue.

Will cutting growth-promoting antimicrobials cut resistance?

Livestock producers and feedlot operators currently have four ways to use antimicrobials on their cattle:

1. to treat sick animals;

2. to control the spread of illness in the herd;

3. to prevent illness in healthy animals that are likely to be exposed to a pathogen; and,

4. to promote growth by altering the gut flora.

However, regulatory changes from the federal government, expected in 2017, will likely put an end to growth promotion claims on antimicrobials. That change is designed to reduce antimicrobial resistance.

The new regulations won’t wipe out a huge number of antimicrobials. Many growth promoters also have other label claims, Campbell said, so they’ll still be available for other uses, such as preventing disease.

While cutting growth-promoting antimicrobials seems like it should reduce resistance, that might not be the case. Denmark studied the effects of eliminating growth promoting antimicrobials between 2001 and 2010. The livestock industry did use fewer Category 3 antimicrobials. But Danes had to treat more sick animals, using more of the high-importance antimicrobials.

Denmark has an amazing system for collecting and organizing data from farmers, Campbell said, and no one can match that data.

But others have looked at similar issues, along with links between animal drugs and antimicrobial resistance in humans, Campbell said. Researchers have found links between antimicrobial use in poultry, and resistant microbes in people, in both the U.S. and Canada, he added.

For example, a 2010 study found a strong correlation between ceftiofur-resistant Salmonella infections in humans and ceftiofur-resistant Salmonella in retail chicken. In Quebec, the same researchers found a link between ceftiofur use in hatcheries and fluctuating levels of resistant E. coli and Salmonella in retail chicken. Ceftiofur is a Category 1 antibiotic.

Canadian chicken farmers voluntarily stopped using Category 1 drugs in 2014. Since then, buyers are pushing North American chicken producers to further limit antimicrobial use or stop altogether. Flocks are being hit with a 20 per cent higher mortality rate, Campbell said. It’s taking 10 more days to get chickens to market. And producers are treating more flocks with antimicrobials because birds are getting sick, Campbell added.

Society can’t afford to ignore antimicrobial resistance. But controlling it will be a long-term effort, he said. “And we may have some hiccups along the way. Some unintended consequences as we go, too.”

The 2010 study on antimicrobial-resistant microbes in chicken is available online.

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.



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