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

In animals/agriculture

Antibiotics are used on a large scale in animals and agriculture. As in human medicine, some of this use is prudent, while some is improper. Any antibiotic use can promote survival and spread of resistant bacteria.

Why are antibiotics used in animals and agriculture?

  • To treat diseases in animals. Treatment can be given to individual animals or to groups of animals.
  • To prevent disease in larger groups of healthy animals:
    • Under specific circumstances, such as in the face of an outbreak of disease
    • Routinely
  • To promote growth of food animals.
  • To prevent bacterial infections when growing fruits and vegetables. Antibiotics are sometimes sprayed on or injected into fruit and vegetable crops.

Route of treatment depends largely on the animal species and the type of production system. Pigs and poultry are frequently given antibiotics orally through feed or water, especially when kept in large units. Individual treatment is more common in smaller units and for ruminants.

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?

  • Food animals are exposed to antibiotics through different routes as described above, as well as through the environment. 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 fail.

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 for 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 Article that summarizes 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?
Drugs make bugs 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).
Tackling AMR in Bangladesh – a One Health approach Video from FAO that describes how antibiotics are used in food animal production in Bangladesh. Outlines how AMR is tackled through a One Health approach by the Bangladesh Antimicrobial Resistance Alliance.
Raising pigs & problems – saying no to antibiotics in animal feed Video. 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 Video. TEDx talk by Lance Price describing antibiotic use in factory farms and what actions to take to make a change (13 min).

More from "Use and inappropriate use"

FAO. Tackling AMR in Bangladesh - a One Health approach [Internet]. 2018 [cited 2021 Jan 8]. Available from:
Hoelzer K, Pew Charitable Trusts - PEW. Link Reaffirmed Between Antibiotic Use in Animal Agriculture and the Public Health Risk [Internet]. 2017 [cited 2018 Dec 8]. Available from:
Tang KL, Caffrey NP, Nóbrega DB, Cork SC, Ronksley PE, Barkema HW, et al. Restricting the use of antibiotics in food-producing animals and its associations with antibiotic resistance in food-producing animals and human beings: a systematic review and meta-analysis. The Lancet Planetary Health [Internet]. 2017 Nov 1;1(8):e316–27. Available from:
European Medicines Agency. Updated advice on the use of colistin products in animals within the European Union: development of resistance and possible impact on human and animal health [Internet]. 2016. Available from:
Liu Y-Y, Wang Y, Walsh TR, Yi L-X, Zhang R, Spencer J, et al. Emergence of plasmid-mediated colistin resistance mechanism MCR-1 in animals and human beings in China: a microbiological and molecular biological study. Lancet Infect Dis [Internet]. 2016 Feb;16(2):161–8. Available from:
Boeckel TPV, Glennon EE, Chen D, Gilbert M, Robinson TP, Grenfell BT, et al. Reducing antimicrobial use in food animals. Science [Internet]. 2017 Sep 29 [cited 2017 Oct 24];357(6358):1350–2. Available from:
Raising pigs & problems -- saying no to antibiotics in animal feed: David Wallinga at TEDxManhattan [Internet]. 2012 [cited 2015 Apr 10]. Available from:
Factory farms, antibiotics and superbugs: Lance Price at TEDxManhattan [Internet]. 2014 [cited 2015 Apr 10]. Available from:
Centers for Disease Control and Prevention - CDC. Antibiotic Resistance from the Farm to the Table [Internet]. Available from:
The Pew Charitable Trusts. Bibliography on Antibiotic Resistance and Food Animal Production (Scientific Studies 1969-2014) [Internet]. [cited 2015 Feb 11]. Available from:
Skov RL, Monnet DL. Plasmid-mediated colistin resistance ( mcr - 1 gene): three months later, the story unfolds. Eurosurveillance [Internet]. 2016 Mar 3 [cited 2016 Mar 30];21(9). Available from:
Roy Chowdhury P, McKinnon J, Wyrsch E, Hammond JM, Charles IG, Djordjevic SP. Genomic interplay in bacterial communities: implications for growth promoting practices in animal husbandry. Front Microbiol [Internet]. 2014;5:394. Available from:
Drugs Make Bugs [Internet]. 2014 [cited 2015 Apr 10]. Available from: