Too Much of a Good Thing: How Overuse of Antibiotics on Farms is a Threat to Human Health

There are over 70,000 thousand hogs and pigs in the U.S. Each pig has more than 7 million bacterial genes in its gut. Some of them are great and most of them are inconsequential but a few are the cause of international alarm. That’s because they have evolved resistance to antibiotics — antibiotics that are necessary for treating human infections. In 2014 pharmaceutical companies sold nearly 21 million pounds of medically important antibiotics for use in animal feed, more than three times the amount sold for use in people (1). Antibiotics are given to animals to protect them from disease, but they are also used to help farm animals grow faster on less food. And when antibiotics are used in such a concentrated manner they kill of all the susceptible bacteria, thereby selecting for the mutants that are resistant to the antibiotics. The resistant bacteria, whose competition has now been eliminated, can now replicate freely and become the majority of that bacteria population.

And this is bad; not just because these drugs will no longer work for animals, but also because they will no longer be effective for treating humans. Once resistant bacteria has been selected for in animals, it is only a matter of time before it is spread from animal feces to farm workers. In one study, MRSA, a bacterium that has spread all over American hog farms, and which has become resistant to several major classes of antibiotics, was found growing in the nostrils of 64 percent of farm workers (1). Animal feces is also used to fertilize crops, which means that bacteria is spread through the soil used to grow food. In a study conducted in Pennsylvania, people who lived near crop fields treated with pig manure had more than 30 percent increased odds of developing MRSA infections compared with people who were least exposed (1). In one study scientists were able to collect drug resistant microbes by driving behind chicken transport trucks (1). And even if bacteria that was not directly targeted by antibiotics can still develop resistance. Research shows that segments of DNA which code for drug resistance can jump between different species and strains of bacteria with surprising ease (1). The resistance gene is on a DNA ring called a plasmid that can be easily transferred from one bacterial species to another, thereby exacerbating the issue.

Some of these drugs used on farms are for illnesses that are easily treatable today, but if the antibiotics are rendered ineffective, then bacterial infections such as pneumonia and bronchitis could turn deadly. Drug resistant infections currently kill about 700,000 people per year and that number could increase to 10 million by 2050 if the drug resistance trend continues unchecked (2). According to the World Health Organization, the rate at which bacteria strains are developing resistance to antibiotics far outpaces the rate at which scientists are developing new medicines to kill the strains (3). In 2017, the FDA banned the use of antibiotics to help livestock gain weight and required meat producers receive a veterinary prescription to use antibiotics to treat and prevent disease (2). But critics say that these rules do not do enough to prevent the spread of drug resistant bacteria. Farmers can still use antibiotics for “disease prevention and control.” In many industrial farms, in order to maximize space animals are kept in very close quarters, conditions which render them particularly vulnerable to disease. In 1992 only 30 percent of farms raised more than 2,000 hogs at a time but by 2009 farms of this size accounted for 86 percent of the US hog industry (1).

The good news is that this trend is reversible. A team of researchers from the University of Maryland School of Public Health isolated Enterococcus bacteria from feed, water, and litter collected at five organic poultry farms in the mid atlantic. All of these farms had recently converted from conventional techniques and were raising their first flock of organic animals. Compared to the strains collected from conventional farms, E. faecalis strains collected from organic farms were less likely to be resistant to 20 microbials with significant differences for 7 compounds (3). For erythromycin, a common antibiotic, 67 percent of an enterococcus bacterium from conventional poultry farms were found to be resistant while 18 percent were resistant from organic farms (4). The percentages of multidrug resistant bacteria were also significantly lower among bacteria from organic versus conventional farms (3). These promising results suggest that at least some antibiotic resistance can be quickly reversed by switching to organic practices. This is especially true since resistance comes at a cost. The mutations reduce the cellular energy a microbe uses to reproduce so while individuals have a better chance of surviving the population grows more slowly. If bacteria are no longer exposed to antibiotics, they ditch their resistant genes over generations (1).

The demand for organic meat products is growing with increased consumer awareness concerning the benefits of organic practices. U.S. retail sales of organic meat and poultry jumped 32 percent to $569 million in 2015 according to the power of meat survey released by the Food Marketing Institute and the North American Meat Institute. But organic meat and poultry still only account for 3.8 percent of packaged meat up from less than one percent in 2010. Chicken has the highest share of organic at 6.7 percent but the share of organic pork is only .4 percent (5). There is still progress to be made but if consumer demand for organic meat continues to increase there is promising potential to reverse this trend and ensure that antibiotics remain effective.

1. Moyer, Melinda Wenner. “How Drug-Resistant Bacteria Travel from the Farm to Your Table.”Scientific American, 1 Dec. 2016, www.scientificamerican.com/article/how-drug-resistant-bacteria-travel-from-the-farm-to-your-table/.
2. Moodie, Alison. “Will New FDA Rules Curb the Rise of Antibiotic-Resistant Superbugs?” The Guardian, Guardian News and Media, 8 Jan. 2017, www.theguardian.com/sustainable-business/2017/jan/08/fda-antibiotic-use-in-livestock.
3. Holtcamp, Wendee. “Poultry Relief? Organic Farming May Reduce Drug Resistance.”Advances in Pediatrics., U.S. National Library of Medicine, Nov. 2011, www.ncbi.nlm.nih.gov/pmc/articles/PMC3226524/.
4. Barclay, Eliza. “Organic Poultry Farms Have Fewer Drug-Resistant Bacteria, Study Finds.”NPR, NPR, 10 Aug. 2011, www.npr.org/sections/health-shots/2011/08/10/139386917/organic-poultry-farms-have-fewer-drug-resistant-bacteria-study-finds.
5. “U.S. Organic Meat and Poultry Market Examined.” Stanford Study Confirms Why Organic Is so Popular, Says OTA, 1 Mar. 2016, www.sustainablefoodnews.com/printstory.php?news_id=24661.