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How did we end up here?  –  Use and inappropriate use

In animals/agriculture

Antibiotics are used also in animals and agriculture. As in human medicine, some of this use is prudent, while some is improper. Any antibiotic use runs the risk of promoting survival and spread of resistant bacteria.

Why are antibiotics used in animals and agriculture?

  • To treat diseases in animals (terrestrial and aquatic), and to curb outbreaks of clinical disease by treatment of larger groups of animals.
  • Routinely to prevent disease in large groups of healthy animals (terrestrial and aquatic).
  • To increase the growth rate of the animals (growth promotion).
  • To treat or prevent bacterial infections when growing fruits and vegetables. Antibiotics are sometimes sprayed on or injected into fruit and vegetable crops.

Global antibiotic consumption in livestock was estimated at 131,000 tons in 2013. When antibiotics are used in settings where animals are kept in close proximity under unhygienic conditions, it creates a perfect environment for selection and spread of resistant bacteria.

How do animals acquire resistant bacteria?

  • Animals are exposed to antibiotics through different routes and for different reasons as described above. Antibiotic exposure promotes survival and spread of resistant bacteria in the animals.
  • Animals may be infected with already resistant bacteria from the animal handlers. For example, a human carrying MRSA can infect the udder of a cow.
  • Resistant bacteria can be transmitted from animals to animals, particularly when there is a resistant infection going through the herd.

What are the consequences for human health?

Scientists have provided evidence that antibiotic use in the animal/agricultural sector is a contributing factor in the development and spread of antibiotic resistant bacteria in animals and the environment, as well as for some of the resistance we see in human pathogenic bacteria. Read more in Antibiotics in the environment.

Consequences for human health – The example of colistin resistance

Colistin was used in human medicine between the 1950s and 1970s, after which its use diminished as safer drugs were developed. It was however not completely abandoned, and with increasing rates of multidrug-resistance, colistin was revived and recognized as a critically important antibiotic to be used as a last resort when all other therapies failed.

Meanwhile, colistin was marketed to farmers both for treatment and prevention of disease and in some countries also for growth promotion. Unfortunately, colistin use in agriculture lead to selection of resistance. When the mcr-1 gene was discovered, a potential disaster became apparent. mcr-1 provides colistin resistance and is located on a plasmid, a mobile genetic element. This makes it transferrable between different strains and even species of bacteria. Now, bacteria with mcr-1, along with several variants of the gene, have been found worldwide in the environment, animals and humans – even causing disease in patients.

Higher abundance of the mcr-1 gene in isolates from food animals compared to human isolates, the much higher use of colistin in animal farming compared to human medicine, and the finding of mcr-1 together with genetic elements typically seen in animal environments, indicates a flow from animals to humans.

Below is a selection of resources introducing the magnitude and scope of the problem.

Selected Resources

Resource Description
Antibiotic resistance from the farm to the table Infographic from CDC that describe what happens when antibiotics are used in food-animal production, and how antibiotic resistant bacteria can spread to humans via food and the consequences.
Link Reaffirmed Between Antibiotic Use in Animal Agriculture and the Public Health Risk Summary of the main points from the review article ‘Antimicrobial drug use in food-producing animals and associated human health risks: what, and how strong, is the evidence? Link to article in text.
Drugs make bugs Short video describing how and why antibiotic-resistant superbugs may arise in animal farms where antibiotic usage is high and how they can spread in the environment (3 min).
Raising pigs & problems – saying no to antibiotics in animal feed D. Wallinga speaks at TEDx-Manhattan about the use of antibiotics in animal feed and the consequences (13 min).
TEDxManhattan: Factory farms, antibiotics and superbugs TEDx talk by Lance Price describing antibiotic use in factory farms and what actions to take to make a change (13 min).

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