Antimicrobial Resistance 101

What is the Problem?

Anytime anyone uses an antimicrobial, be it in a human or an animal, it kills off the bacteria that are susceptible to that drug and leaves the resistant ones behind. It's the same concept as "natural selection" and "survival of the fittest". When the susceptible bacteria are wiped out, the resistant ones have room to grow and multiply, and before you know it you have the same number of bacteria again, but the antimicrobial that was used before doesn't work anymore. People are causing the antimicrobial-resistant bacteria to be "selected" for survival at a very rapid rate through frequent use of antimicrobials.

Some bacteria are also able to share the pieces of their DNA (genes) that make them resistant. Often called "Superbugs", these bacteria often have large sets of these genes that they've accumulated over time, making them resistant to most or all available antibiotics, leaving little or no way to treat the infected person or animal.

The main concern with antimicrobial-resistant bacteria is their spread to and infection of people in the community. While anyone can be infected, those most vulnerable include patients in hospitals and long-term care facilities, and individuals whose immune systems may not work as well due to age or illness. Animals can also get sick from infection with resistant bacteria. This is not only a concern from an animal welfare and production standpoint, but they also frequently carry these bacteria without showing clinical signs, making them a potential source for spread of these microbes to people. Even people who never touch a farm animal can come in contact with bacteria from livestock through the environment, water sources, animal-based food products, and even non-animal-based food products (e.g. fruits and vegetables that have been fertilized with animal manure, or cross-contaminated after harvest).

What Action is Being Taken?

Countries all over the world are taking action to try to reduce antimicrobial use (AMU) - in both humans and animals - in order slow the emergence of antimicrobial resistance (AMR). The World Health Organization has a global action plan to address AMR.

On the agriculture side, many European countries are already taking measures to reduce AMU, and the US and Canada are making efforts to join in a global struggle against AMR. Following a similar announcement by the US Food and Drug Administration, Health Canada is eliminating the use of medically important antimicrobials as growth promotants in livestock and poultry, by having drug companies remove the label claims on such products. Table 1 shows Health Canada's categorization of antimicrobials used in livestock production.

Medically important antimicrobials used in feed or water will also no longer be available to producers over-the-counter without a prescription from a veterinarian. Importation of these drugs for a producer's own use will also no longer be allowed, and importation of active pharmaceutical ingredients (i.e. drugs that need to be mixed or compounded before being administered) will also be more tightly controlled.

While all these changes continue to take shape, it is critical for producers to stay in close contact with their industry organizations to ensure that your interests and concerns are properly addressed.

Table 1. Categorization of antimicrobials by importance to human medicine (according to Health Canada)

Category of importance to human medicine
Antimicrobial class
I - Very High
Cephalosporins (3rd & 4th generation)
Penicillin-B-lactamase inhibitor combos
Amoxicillin & Clavulanic acid
Polymyxin B (Colistin)
Few / none
II - High
Cephalosporins (1st & 2nd generation)
Gentamicin, Streptomycin
Erythromycin, Tylosin
Penicillin G, Ampicillin
III - Medium
variety of sulfa-drugs
For some
IV - Low
Monensin, Lasalocid

What can I do to help?

Every person has a role to play in helping to stem the rising tide of antimicrobial resistance. Work with your veterinarian to ensure you have effective biosecurity practices in place to minimise the risk of disease introduction and spread. Keeping your livestock healthy by providing good nutrition, a clean low-stress environment, clean air (i.e. good ventilation) and avoiding issues like over-crowding can significantly reduce the need to use antimicrobials in the first place. When antimicrobials are needed, use them wisely to ensure each use is as effective and efficient as possible. (See tips below.)

Tips for Reducing Illness and the Need for Antimicrobial Use

  • Reduce stress: strategies such as preconditioning and low-stress weaning take some extra time and effort, but can certainly be worthwhile especially in terms of reducing the need for antimicrobials. Low-stress handling and avoiding things like overcrowding are also important for animal welfare.
  • Biosecurity: it's often not possible to avoid some situations like mixing of animals from different production stages, but reducing the amount of mixing whenever and as much as possible can still be very beneficial. Also be sure to separate sick animals promptly to reduce the spread of infection.
  • Vaccinate: vaccination helps prevent disease before it starts, and "herd immunity" can even help protect unvaccinated animals by reducing the amount of bacteria and viruses circulating in a group.
  • Talk to your veterinarian: you and your veterinarian are the best team to identify the specific strengths and weaknesses on your operation that are the most critical to reducing antimicrobial use and improving animal health while maintaining profitability.

Tips for using antimicrobials wisely when they're needed

  • Know what you're treating: antimicrobials only work on bacteria, not viruses, and some conditions (for example lameness) can be caused by things other than infection.
  • Pick the right product: don't crack a walnut with a sledgehammer. Avoid pulling out a powerful broad-spectrum antimicrobial when there's a drug that will more specifically target the infection you're trying to treat. This is often better for the animal and it's better for reducing the risk of resistance overall.
  • Follow instructions: make sure you use the appropriate dose and route, and treat the animal for the right number of days. This will maximize the effectiveness of the antimicrobial, and avoid residues when the standard withdrawal time is observed.
  • Treat sick animals promptly: this typically results in a better response and decreases the need for additional treatments.
  • Keep good records: the only way to know for sure if your strategies and treatment regimens are working consistently is to keep track of what animals get sick, how they are treated, and how they respond. This information should be reviewed regularly with your veterinarian to help ensure antimicrobials are being used in the most effective way possible, and to identify any other areas where preventative strategies could be used or improved.
  • Know when to euthanize: don't use antimicrobials to treat an animal that is unlikely to survive as a "last ditch effort". Save the antimicrobials for the cases in which they are likely to be effective.

Additional resources and information

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