Antibiotic resistance occurs when bacteria undergo changes that enable them to resist antibiotics that previously were effective treatments. This makes certain bacterial infections difficult to overcome.[1]
Antibiotic resistance is an inevitable and natural process due to the huge numbers of microbes and their inherent ability to adapt. But the process can be sped up by the “aggressive and persistent use” of antibiotics.[2]
Antimicrobial resistance is a broader term that encompasses resistance not only to antibiotics but also to other medicines used to treat a range of infections caused by bacteria, parasites, viruses, and fungi.[3] Often the terms are used interchangeably.[4,5] We use and focus on “antibiotic resistance” in these posts.
Cleveland Clinic (2023) Antibiotic Resistance. https://my.clevelandclinic.org/health/articles/21655-antibiotic-resistance
Michael, C. A., et al., (2014). The antimicrobial resistance crisis: causes, consequences, and management. Frontiers in Public Health, 2, 145–145, p. 2.
World Health Organization, Antimicrobial resistance. https://www.who.int/health-topics/antimicrobial-resistance
US Food and Drug Administration. (2012). Guidance for Industry: The Judicious Use of Medically Important Antimicrobial Drugs in Food-Producing Animals, p. 4. [“The broader term “antimicrobial,” commonly used in reference to drugs with activity against bacteria, is used in this document interchangeably with the terms antibacterial or antibiotic.”]
Sneeringer, S., et al., (2015). Economics of antibiotic use in US livestock production. USDA, Economic Research Report, p. 2. [“In this report, we generally use the term ‘antibiotics’ interchangeably with ‘antimicrobials.’”]
All uses of antibiotics reduce their efficacy.[1] As the CDC plainly states, “Simply using antibiotics creates resistance.”[2] Many sources refer to “overuse” to describe the primary cause of resistance.[3]
Microbial communities are renowned for their ability to adapt quickly and effectively. When they are exposed to treatment drugs, “only the microbes able to survive and reproduce will predominate within the microbial community, so causing their ‘advantage’ to become common. More aggressive and persistent use of antimicrobials increases the selective pressure on the microbial community to which they are applied, generating more adaptive solutions to the applied stress, faster.”[4]
U.S. Dept. of Health and Human Services, CDC (June 3, 2024) A Complex Web: Everything is Connected, Food, Farms, & Animals, CS 320128-F. [“However, any time antibiotics are used, the drugs contribute to the development of antibiotic resistance.”]
U.S. Dept. of Health and Human Services, CDC (2013) Antibiotic Resistance Threats in the United States, 2013, U.S. Dept. of Health and Human Services, p. 14.
Ventola, C. L. (2015). The antibiotic resistance crisis: part 1: causes and threats. P&T (Lawrenceville, N.J.), 40(4), 277–283, p. 278. [“The overuse of antibiotics clearly drives the evolution of resistance. Epidemiological studies have demonstrated a direct relationship between antibiotic consumption and the emergence and dissemination of resistant bacteria strains.”]
Michael, C. A., et al., (2014). The antimicrobial resistance crisis: causes, consequences, and management. Frontiers in Public Health, 2, 145–145, p. 3.
Yes. Antibiotic resistance spreads internationally; it is a global problem that requires global solutions.[1]
China is by far the largest user of antibiotics for animal food production, with ~45% of total usage. Brazil is 2nd at ~8%, and the U.S. is 3rd at ~7%.[2]
Because of the global nature of antibiotic resistance, it can be considered, “somewhat analogous to climate change, and that suggests that an intergovernmental panel, akin to the Intergovernmental Panel on Climate Change, could be an appropriate vehicle to actively address the problem.”[3] However, there is evidence that the U.S. has helped to slow international efforts to address antibiotic use in farmed animals.[4,5]
World Health Organization (2016) Antimicrobial resistance – a global epidemic, p. 1.[“Globalization fuels the spread of antimicrobial resistance where transmission is facilitated by increased trade, travel and both human and animal migration.”]
Tiseo, K., et al., (2020). Global trends in antimicrobial use in food animals from 2017 to 2030. Antibiotics, 9(12), 918, p. 3.
Woolhouse, M., et al., (2015). Antimicrobial resistance in humans, livestock and the wider environment. Phil. Trans. R. Soc. B, 370(1670), 20140083, p. 1.
Lisa Held (Sept. 25, 2024) The US Weakens a UN Declaration on Antibiotic Resistance, Civil Eats, https://civileats.com/2024/09/25/the-us-weakens-a-un-declaration-on-antibiotic-resistance/
Natasha Gilbert (Sept. 11, 2024) US pressure weakens global commitments on antimicrobial resistance, U.S. Right to Know. https://usrtk.org/factory-farming/us-pressure-weakens-global-commitments-on-antimicrobial-resistance/
In the U.S., more than 2.8 million antimicrobial-resistant infections occur each year. More than 35,000 people die as a result.[1]
On a global level it is estimated that ~1.3 million deaths are directly attributable to antibiotic resistance.[2]
On an individual level, growing resistance means that “an increasing use of older less effective techniques in controlling infections will be required. Such techniques, including debridement, disinfection, amputation, and isolation will mean that the process of treating infections will take longer, be far more invasive, and will be less successful.”[3]
As the CDC explains, “Even when alternative treatments exist, research has shown that patients with resistant infections are often much more likely to die, and survivors have significantly longer hospital stays, delayed recuperation, and long-term disability.”[4]
We are threatened with “a return to the preantibiotic era, where everyday infections relating to childbirth, surgery and open fractured limbs could be potentially life-threatening.”[5]
U.S. Dept. of Health and Human Services, CDC (2019) Antibiotic Resistance Threats in the United States 2019, p. vii.
Murray, C. J., et al., (2022). Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis. The lancet, 399(10325), 629-655, p. 637.
Michael, C. A., et al., (2014). The antimicrobial resistance crisis: causes, consequences, and management. Frontiers in Public Health, 2, 145–145, p. 2.
U.S. Dept. of Health and Human Services, CDC (2013) Antibiotic Resistance Threats in the United States, 2013, p. 5.
Tang, K. W. K., et al., (2023). Antimicrobial resistance (AMR). British Journal of Biomedical Science, 80, 11387, p. 1.
About two-thirds of all antibiotics deemed medically important are used by the factory farming system in the U.S.[1-5]
See Animal Ag Antibiotic Usage for details. The key references follow in footnotes 2-4.
U.S. FDA (2023) 2022 Summary Report On Antimicrobials Sold or Distributed for Use in Food-Producing Animals, Tables 4a & 4b. [Provides farmed animal totals.]
David Wallinga (2022) U.S. Livestock Industries Persist in High-intensity Antibiotic Use, Issue Brief, IB: 22-II-A, National Resources Defense Council. [Note: This report provides human use totals through 2019 as well as excellent overview with key resources. We are not aware of other credible sources for human use figures. Dr. Wallinga is a researcher and recognized expert; NRDC has been at the forefront of research and advocacy in this area.]
David Wallinga (September 2023) Antibiotic Use Remains Far too Intensive in U.S. Livestock, National Resources Defense Council. https://www.nrdc.org/bio/david-wallinga-md/antibiotic-use-remains-far-too-intensive-us-livestock [Provides human use totals through 2020]
U.S. FDA (2022). 2021 Summary Report On Antimicrobials Sold or Distributed for Use in Food-Producing Animals, p. 3, fn 1. [Medically important antimicrobials, “are those antimicrobials that have been determined to be medically important to human medicine.”]
Despite the widespread use of antibiotics by animal ag, the extent to which antibiotic resistance in humans can be attributed to animal usage is apparently complex and somewhat controversial.[1,2] Unchallenged is that animal ag is a significant source.[3]
There is no question that major usage in animals is “the primary driver for the accumulation of harmful resistance genes in the animal reservoir,” thereby worsening animal health.[4] Eventually this resistance in animals moves to human populations.[5]
As some reports imply, arguing that we must have more evidence before taking action is akin to standing in front of a tunnel trying to determine if the rapidly approaching bright light is affixed to a train.[6,7]
Murray, C. J., et al., (2022). Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis. The lancet, 399(10325), 629-655, p. 649. [“Increased use of antibiotics in farming has been identified as a potential contributor to AMR in humans although the direct causal link remains controversial.”]
Chang, Q., et al., (2015). Antibiotics in agriculture and the risk to human health: how worried should we be? Evolutionary applications, 8(3), 240-247, p. 244. [“The topic of agricultural antibiotic use is complex… As we noted at the start, many believe that agricultural antibiotics have become a critical threat to human health. While the concern is not unwarranted, the extent of the problem may be exaggerated.”]
Tang, K. L., et al., (2017). 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, 1(8), e316-e327, p. e324. [“…meta-analysis of 13 studies showed similar results, with a 24% absolute reduction in the prevalence of antibiotic-resistant bacteria in humans with interventions that reduce antibiotic use in animals.”]
Van Boeckel, T. P., et al., (2017). Reducing antimicrobial use in food animals. Science, 357(6358), 1350-1352, p. 1350.
Van Boeckel, T. P., et al., (2019). Global trends in antimicrobial resistance in animals in low-and middle-income countries. Science, 365(6459), eaaw1944. Abstract [“Escalating resistance in animals is anticipated to have important consequences for animal health and, eventually, for human health.”]
O’Neill, J. (2015). Antimicrobials in Agriculture and the Environment: Reducing Unnecessary Use and Waste. The Review on Antimicrobial Resistance, London, p. 10. [“But given all that we know already, it does not make sense to delay action further: the burden of proof should be for those who oppose curtailing the use of antimicrobials in food production to explain why, not the other way around.”]
Van Boeckel, T. P., et al., (2015). Global trends in antimicrobial use in food animals. PNAS, 112(18), 5649-5654, p. 5. [“Given the potential costs of inaction, this study, among others, calls for urgent and concerted action in all countries, which is needed to limit the overuse and abuse of antimicrobials in food animal production.”]
Factory farms confine highly stressed, densely packed, genetically homogenous animals that eat unnatural diets and live in their own waste – ideal conditions for the spread of disease. Because of these conditions, “antibiotics are an integral part of industrial agriculture and there are very few alternatives.”[1] They are widely considered an “essential component” of systems that “necessitate antimicrobials to keep animals healthy and maintain productivity…”[2,3]
The immediate goals of routine antibiotic use are to treat and prevent disease, promote growth, increase feed conversion, and support uniformity of weight for slaughter.[4-6]
The over-riding goal is to increase production while reducing costs, and thereby maximize profits.[7] Producers are incentivized to use antibiotics as long as there are no strict government regulations and few consumers willing to pay a premium for antibiotic-free options.
Although use for growth promotion is no longer allowed in the U.S.,[8] it is impossible to eliminate, because many antibiotics offer the dual function of growth promotion and disease control.[9,10] Farmers acknowledge still using antibiotics primarily for growth.[11]
Woolhouse, M., et al., (2015). Antimicrobial resistance in humans, livestock and the wider environment. Phil. Trans. R. Soc. B, 370(1670), 20140083, Abstract.
Tiseo, K., et al., (2020). Global trends in antimicrobial use in food animals from 2017 to 2030. Antibiotics, 9(12), 918, p. 1. [“Antimicrobials are an essential component of intensive farming systems…”]
Van Boeckel, T. P., et al., (2015). Global trends in antimicrobial use in food animals. PNAS, 112(18), 5649-5654, p. 1.
Woolhouse, M., et al., (2015), p. 2. [“Antimicrobials are used on livestock farms for a number of reasons: (i) as therapeutics; (ii)more commonly as metaphylactics, meaning that the presence of clinical illness in one animal triggers drug treatment of the whole herd or flock; (iii) prophylactics; and (iv) growth promotion.”]
Sneeringer, S., et al., (2015). Economics of antibiotic use in US livestock production. USDA, Economic Research Report, p. 4. [“Additionally, production-use antibiotics may reduce weight variability between animals, producing more uniform animals that are better suited to mechanized processing and that generate steadier income streams to farmers.”]
Ardakani, Z. et al., (2023) Global Public Health Cost of Antimicrobial Resistance Related to Antibiotic Use on Factory Farms, World Animal Protection. [See pp. 18-41 for a detailed review of the factors propelling antibiotic usage including animal stressors and diseases, and the factory farm methods and conditions that increase sickness.]
Cromwell, G. L. (2002). Why and how antibiotics are used in swine production. Animal biotechnology, 13(1), 7-27, p. 19. [For pig production, “the net return is $2.99 for each $0.70 invested in the antibiotic.”]
U.S. FDA (February 2024) FACT SHEET: Veterinary Feed Directive Final Rule and Next Steps. https://www.fda.gov/animal-veterinary/development-approval-process/fact-sheet-veterinary-feed-directive-final-rule-and-next-steps
Cameron, A., & McAllister, T. A. (2016). Antimicrobial usage and resistance in beef production. Journal of animal science and biotechnology, 7, 1-22, p. 3. [“Although prophylaxis/metaphylaxis may be a more judicious use of antimicrobials than growth promotion, growth promotion is often a benefit of either treatment.”]
Lisa Held (June 12, 2024) Medically Important Antibiotics Are Still Being Used to Fatten Up Pigs. Civil Eats. https://civileats.com/2024/06/12/medically-important-antibiotics-are-still-being-used-to-fatten-up-pigs/
USDA Animal and Plant Health Inspection Service (July 16, 2024) Swine Part II: Reference of Management Practices on Large-Enterprise Swine Operations in the U.S. https://www.aphis.usda.gov/swine-2021-part-ii-reference-management-practices-large-enterprise-swine-operations-united-states [See: Individual Tables, Table C.5.g. Many operations use antibiotics primarily for growth for nursery pigs.]
From the perspective of human suffering, antibiotic resistance is a major externality of industrial animal ag – possibly one of the largest. Remarkably, the high levels of pain, suffering, and financial burdens imposed on millions of Americans have not been enough to induce a sharp reduction of antibiotic usage in farmed animals or a shrinkage in the systems that make antibiotics essential for mass production. It demonstrates our willingness to accept unusually high levels of health risk to maintain the availability of inexpensive meat.[1]
Kirchhelle, C. (2018). Pharming animals: a global history of antibiotics in food production (1935–2017). Palgrave Communications, 4(1), p. 10. [“Probably the most important reason for this story of failure is that many countries have historically favoured reliable access to cheap meat over broader agricultural and antibiotic reform.” “Without challenging the ideals of factory-like production and cheap protein that are still driving antibiotic use, current reforms will have limited success.”]
Antibiotic resistant bacteria from livestock can be transmitted to humans via three routes – environmental, food products, or directly to agricultural workers.[1,2]
About 75% of the antibiotics given to livestock is excreted in manure.[3,4] Antibiotic residues can then be dispersed into surface water and groundwater and can leach into soils.[5]
Van Boeckel, T. P., et al., (2015). Global trends in antimicrobial use in food animals. PNAS, 112(18), 5649-5654, p. 1. [Antimicrobial resistant bacteria “of animal origin can be transmitted to humans through the environment, and food products and to agricultural workers by direct contact.”]
Tiseo, K., et al., (2020). Global trends in antimicrobial use in food animals from 2017 to 2030. Antibiotics, 9(12), 918, p. 1. [“AMR in food-producing animals can also affect humans who work closely with animals or live in the vicinity of a farms. Food products contaminated with drug-resistant bacteria can also potentially affect the health of humans with AMR pathogens. AMU (antimicrobial use) on farms may also contaminate the environment with drug-resistant pathogens that are potentially harmful to humans.”]
Chee‐Sanford, J. C., et al., (2009). Fate and transport of antibiotic residues and antibiotic resistance genes following land application of manure waste. Journal of environmental quality, 38(3), 1086-1108, Abstract.
Robles-Jimenez, L. E., et al., (2021). Worldwide Traceability of Antibiotic Residues from Livestock in Wastewater and Soil: A Systematic Review. Animals (Basel), 12(1), 60, p. 2.
Oliver, J. P., et al., (2020). Invited review: Fate of antibiotic residues, antibiotic-resistant bacteria, and antibiotic resistance genes in US dairy manure management systems. Journal of Dairy Science, 103(2), 1051–1071, pp. 1052-1053.
The most common applications include repeated exposures to low doses, which create ideal conditions for the emergence and spread of ARBs (antimicrobial resistant bacteria) in animals.[1]
“Unlike in humans, antimicrobial use in animals is primarily intended for growth promotion and mass prophylaxis. These uses are often administered both through feed, directly targeting the gut, and in low-dose patterns that promote the evolution of resistance.”[2] Treating all animals in a population, including those that are healthy, with low doses of antibiotics in feed or water drives the selection of resistant bacteria strains. And if the exposure is continued for a period of time, “then resistant strains are advantaged in terms of reproduction and spread.”[3]
Of the medically important antibiotics given to farmed animals, 94% are given in their water or feed; ~63% in their feed, and ~31% in their water.[4]
In large pig operations, medically important antimicrobials are administered in feed on more than 90% of operations.[5] Of large cattle feedlots, about 80% give medically important antibiotics in feed.[6]
Van Boeckel, T. P., et al., (2015). Global trends in antimicrobial use in food animals. PNAS, 112(18), 5649-5654, p. 1.
Van Boeckel, T. P., et al., (2017). Reducing antimicrobial use in food animals. Science, 357(6358), 1350-1352, p. 1351.
Kumar, A. et al., (2018) Sub-therapeutic use of antibiotics in animal feed and their potential impact on environmental and human health: a comprehensive review, Journal of Animal Feed Science and Technology 6, 15-24, p. 18.
U.S. FDA (2023) 2022 Summary Report On Antimicrobials Sold or Distributed for Use in Food-Producing Animals, Sales by Route of Administration, Table 6a.
USDA APHIS (2024) Antimicrobial Use and Stewardship on U.S. Swine Operations, 2017, Overall Antimicrobial Use, p. 14.
USDA Animal and Plant Health Inspection Service (2019) Antimicrobial Use and Stewardship on U.S. Feedlots, 2017, p. 15.