Antibiotic Resistance and Animal Agriculture. What’s the deal?
Updated: Mar 7
Let's start with defining antibiotic resistance.
Antibiotic resistance is defined as the ability of organisms (i.e. bacteria) to continue to grow and multiply despite being exposed to a drug that would typically be able to stop and kill (bactericidal) or prevent further replication (bacteriostatic) of bacteria.
What is the science behind it?
First, let’s discuss antibiotics. Antibiotics can be broken down into different classes based on their mechanism of action. For example, β-Lactam antibiotics (i.e. penicillins, carbapenems, cephalosporins) work at inhibiting the cell wall of the bacteria by binding to enzymes (penicillin binding proteins or PBPs) which prevents the last step of cross linking in peptidoglycan synthesis. The term beta-lactam refers to the beta-lactam ring of the antibiotic composition. Bacteria are extremely fast replicating organisms. Faster division can mean they are also able to change their DNA composition much quicker (i.e. gene mutation). And this can help cause…resistance! These bacteria are some smart bugs, let me tell ya. They manipulate their PBPs or produce enzymes called beta lactamases that can essentially breakdown the antibiotic, causing it to no longer take its effect to kill the bacteria.
What does this have to do with meat consumption?
Approximately 80% of antibiotics in the U.S are used for animal and livestock agriculture/aquaculture annually. This does not include veterinary medicine. Animals raised for human consumption are fed antibiotics in order to promote growth, reduce their risk of illness, or increase feed efficiency. Animals and humans naturally carry gut flora and while the doses may be low, chronic exposure doesn’t come without consequence. This inappropriate use leads to resistance. Animal waste and defecation carries these resistant bacteria and once slaughtered, it ends up in the food supply. Through soil, water, and fertilizers, animal defecation can also contaminate other produce such as fruits and vegetables, which ultimately causes human exposure. Not to mention, “antibiotic-free” animal meat or dairy is not standardized in the U.S or approved by USDA, so it cannot be guaranteed that these animals are not exposed to antibiotics; in fact ,natural gut flora of animals still contains some resistant bacteria by default. When patients are actively fighting infections and are in need of prescription antibiotics (over prescribing will be a topic of discussion in the future), there are solutions in place such implementing programs that improve the antibiotic stewardship policies to allow for more appropriate ways to manage and reduce resistance. For example, determining specific antibiotics to utilize for specific infections based on lab cultures, rapid organism identification, susceptibility patterns and resistance trends at an institution through antibiograms. However, what about when we don’t have infections? How can we reduce resistance? Correlations suggest limiting or omitting animal meat and dairy consumption. By eliminating meat consumption, the gut microbiome is significantly altered as well. In terms of clinical impact, the link is plausible for direct human impact, but extensive studies are still needed for conclusive data. One common correlation being UTIs and food-borne resistant E.Coli. The FDA recognized resistance issues and banned use of fluoroquinolones in poultry. However, banning clinically utilized antibiotics for humans comes with complex issues.
Antibiotic resistance, Food, and Food Producing Animals. Centers for Disease Control and Prevention Website. https://www.cdc.gov/features/antibiotic-resistance-food/index.html Updated November 5, 2019.
Chang Q, Wang W, Regev-Yochay G, Lipsitch M, Hanage WP. Antibiotics in agriculture and the risk to human health: how worried should we be?. Evol Appl. 2015;8(3):240–247. doi:10.1111/eva.12185
Economou V, Gousia P. Agriculture and food animals as a source of antimicrobial-resistant bacteria. Infect Drug Resist. 2015;8:49–61. Published 2015 Apr 1. doi:10.2147/IDR.S55778
McGill University.Retail meat linked to urinary tract infections: Strong new evidence. ScienceDaily. Retrieved Jan 21, 2020 from www.sciencedaily.com/releases/2010/01/100120144005.htm
Nordstrom L, Liu CM, Price LB. Foodborne urinary tract infections: a new paradigm for antimicrobial-resistant foodborne illness. Front Microbiol. 2013;4:29. Published 2013 Mar 6. doi:10.3389/fmicb.2013.00029
Hollis A., Ahmed Z. Preserving Antibiotics, Rationally. N Engl J Med 2013; 369:2474-2476 DOI: 10.1056/NEJMp1311479
Reid CJ, McKinnon J, Djordjevic SP. Clonal ST131-H22 Escherichia coli strains from a healthy pig and a human urinary tract infection carry highly similar resistance and virulence plasmids. Microb Genom. 2019;5(9):e000295. doi:10.1099/mgen.0.000295
Shea K.M. Antibiotic Resistance: What Is the Impact of Agricultural Uses of Antibiotics on Children’s Health? PEDIATRICS. 2003; 112(1): 253-258.