Your Reading List

Agriculture And Antimicrobial Resistance: Maybe? Maybe Not?

The origin and cause of antimicrobial resistance (AMR) continues unabated with no end in sight. The urgency of finding answers cannot be overstated and finding answers to a problem as perplexing and complicated as AMR is elusive.

Agriculture is just beginning to recognize the critical role disease surveillance plays along with the ability to measure antimicrobial resistance in an objective and scientifi manner. Also factored into the mix are things like the constant flux of resistance genes in the environment from animals and people, the contribution companion animals have in AMR and the impact items like household sanitizers may have in the equation.

Antibiotics started as a miracle for animal and human medicine with Fleming’s discovery of penicillin in 1928. With its commercial production in the 1940s, antimicrobial use quickly evolved into overdependence.

Thirty years ago the supply of effective antibiotics seemed endless, to the point a confident scientificommunity predicted the eventual elimination of many bacterial pathogens. The experts were partially right, but rather than disappearing, the bugs changed. Bacterial infections that responded to first-generation antimicrobials mutated into predators that didn’t respond to anything.

Antibacterials started to fail. With time the stream of highly resistant bacteria outstripped the supply of new drugs to the point that AMR threatened human medical and surgical wards and, single-handedly, changed the rules on how food would be produced.

The Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS) tracks trends in antimicrobial use and resistance patterns of selected species of enteric bacteria obtained at different points in the food chain and from human cases.

The CIPARS annual report profiles antimicrobials considered important in human medicine. At the centre of public debate are two Category-1-related drugs (highly valued as human antimicrobials), ceftiofur a third-generation cephalosporin and ciprofloxacin a fluoroquinolone. Cited in the report are other resistance bacteria linked to agriculture’s use of antimicrobials, the EU’s use of avoparcin and vancomycin-resistant entercocci, emerging methicillin-resistant Staphylococcus aureus in pork and beef and resistantE. coliand salmonella strains.

There is a growing body of evidence indicating continued use of certain antimicrobials in food animals may contribute to the appearance and transference of resistant genes amongst microbes in our environment and ultimately between pathogens affecting both animals and humans. Resistant bacteria or genes generated from human antimicrobial use may actually find their way into animal reservoirs.

Many blame the use of antimicrobials in feed at sub-therapeutic doses for growth promotion and disease prevention as a major cause of AMR. On a tonnage basis, nearly one-half the weight of all antimicrobials made in a year end up being fed to animals in North America. It can be argued that feed grade compounds like ionophores, penicillin and tetracycline have very limited use in human medicine because they are no longer effective. These same compounds, in the view of some, induce multi-drug resistance through transfer of genetic fragments called plasmids between bacteria, including those ultimately affecting humans.

Most of the antimicrobial resistance found in human bacterial pathogens comes primarily from overuse of antimicrobials in humans. One estimate is that agriculture accounts for two to three per cent of all antimicrobial resistance.

Prudence is the answer to most complicated things. And so it should be for issues associated with AMR. Users of antimicrobials must seek solutions collaboratively.

The medical profession issued nearly 700 medical prescriptions covering all oral antimicrobial classes per 1,000 Canadians in 2007. That translates into approximately 0.7 prescriptions per person — 17 per cent of those were Category- 1 antimicrobials. Meanwhile, 1.6 million kilograms of antimicrobials were distributed in Canada for use in animals. On the positive side, total kilograms of antimicrobials distributed for use by Canadian livestock decreased by 8.4 per cent as a percentage of the 2006 total.

Contributing to the proper and prudent use of antimicrobials in food animals includes:

Knowing the pathogen involved and sensitivity to the antimicrobial being considered

Knowledge of how a particular antimicrobial actually inhibits or kills bacteria

Understanding how each class of antimicrobial is distributed in tissue and eliminated from the body of patients

Information about public safety from exposure to potential drug residues so clients understand the need for and importance of withdrawal times

Cost of therapy including labour for administration and potential production losses as a result of withdrawal times

Off-label dosing regimes not consistent with information printed on the label of approved antimicrobials affects meat and milk withdrawal and places responsibility squarely on the shoulders of the prescribing veterinarian to make appropriate withdrawal recommendations. Canadian gFARAD is a service that veterinarians are encouraged to use for guidance for appropriate withdrawal times for extra-label drug use (



futurearticlescanbesenttoCanadianCattlemen( [email protected]) orWCABP( [email protected]).

About the author


Dr. Ron Clarke

Dr. Ron Clarke prepares this column on behalf of the Western Canadian Association of Bovine Practitioners. Suggestions for future articles can be sent to Canadian Cattlemen ([email protected]) or WCABP ([email protected]).



Stories from our other publications