Monday, March 9, 2015

Antibiotic Resistance: Dust from cattle feed yards carries antibiotics, bacteria, and antibiotic resistance genes.

The emergence of drug resistant bacteria is a growing concern for global public health. Antibiotic resistance occurs when an antibiotic has lost its ability to effectively control or kill bacterial growth.  Every time you take an antibiotic prescribed by your doctor, the sensitive bacteria in your body are killed, but resistant strains may be left to grow and multiply.  These resistant bacteria survive, reproduce, and exchange sections of genetic material with other bacteria so that new generations inherit antibiotic resistant genes. Resistance leads to an increasing number of bacterial infections and treatment failure for even the most common pathogens.  For example, some strains of tuberculosis are now resistant to all available microbial drugs. 

The spread of antibiotic resistance is often associated with overuse and misuse of clinical and veterinary chemotherapeutic agents.  It is estimated that over one-half of the antibiotics in the United States are used to food animal production.  All animals carry bacteria in their intestines.  When animals treated with antibiotics are slaughtered and processed, resistant bacteria can contaminate the meat and other animal products.  Resistant bacteria in animal excretion are transported through the environment via runoff, leaching, and land application of manure.  Resistant bacteria can be transferred to the general population via food, and several studies link antibiotic use in food animal production to resistant infections in humans.

US Department of Health and Human Services. "Antibiotic resistance threats in the United States, 2013." Atlanta: CDC (2013).

McEachran et al., researchers from The Institute of Environmental and Human Health at Texas Tech University, characterize a new transmission method: aerial transport via particulate matter from open-air beef cattle farms.  They found evidence of antibiotics, feedlot-derived bacteria, and DNA sequences that encode for antibiotic resistance genes in dust collected downwind of beef cattle feed yards in the Central Plains Region of the United States.  Three tetracycline antibiotics, including tetracycline, chlortetracycline, and oxytetracycline, were detected together in the majority of particulate matter samples downwind of feed yards.  Furthermore, significant levels of six targeted tetracycline resistant genes were also found downwind of feed yards.  Tetracylines are broad-spectrum antibiotics commonly used in animal agriculture on beef cattle, chickens, dairy cattle, turkeys, and swine.  

As of 2014, over 76% of all large-scale (greater than 1,000 head of cattle) beef cattle operations in the U.S. were located in Texan, Oklahoma, Kansas, Nebraska, and Colorado.  The climatic conditions in this semi-arid region are notorious for the high frequency of dust storms.  Feed yard pen floor material, which consists primarily of urine and fecal material, often becomes dry and brittle, and thus susceptible to suspension into the air via wind.  Tetracycline compounds can bind tightly to soil particles and likely remain tightly bound to airborne particulates.  Alarmingly, the antibiotics and bacteria present on the dust and particulate matter have the potential to spread far from their original starting point on the feedlot.  Given the half-lives of tetracycline antibiotics in soil range from 30-180 days, it is possible that they remain active during aerial transport and after deposition onto soil, water, or other surfaces for days to weeks.
McEachran et al. helped explain a previously uncharacterized pathway by which antibiotic resistant bacteria could travel long-distances into places inhabited by humans.  However, further research is needed to consider human health impacts, how far the particulate matter can travel, and if microbes remain viable after aerial transport.  The relationship between antibiotic resistant infections in humans and antibiotic use in animal agriculture is complex, and the battle against antibiotic resistance is far from total victory.

Mercy For Animals.

Andrew D. McEachran, Brett R. Blackwell, J Delton. Hanson, Kimberly J. Wooten, Gregory D. Mayer, Stephen B. Cox, Philip N. Smith. Antibiotics, Bacteria, and Antibiotic Resistance Genes: Aerial Transport from Cattle Feed Yards via Particulate Matter. Environmental Health Perspectives, 2015; DOI: 10.1289/ehp.1408555
Centers for Disease Control and Prevention.  Antibiotic/Antimicrobial Resistance.

Alliance for the Prudent Use of Antibiotics. Antibiotics in Agriculture.


  1. Great topic! Love the shoutout to drug resistance in TB. I think that the scariest thing about all of this is in terms of drug development we are currently unable to keep pace with the increasing numbers of resistant bacteria. I read a few articles recently where scientists were beginning to throw around the term post-antibiotic era, which is terrifying to think about. I think another interesting component to the overuse of antibiotics in factory farms is the rise of the middle class in countries like China and India. This rise is correlated with increased consumption of meat, which leads to more factory farms and greater abuses of current antibiotics.

  2. Even if a link was established between the use of antibiotics on farms and the rise of antibiotic resistance bacteria in humans, I would be surprised if practices were to change. Farms use antibiotics to increase the weight of their animals so consequently price is less since supply is greater. The negative economic impacts of not using antibiotics on farms would definitely discourage action from being taken. Additionally, the agricultural industry has political sway from lobbyists and those in power want to protect their donors. The post-antibiotic era seems to be a very plausible future.

  3. I thought this article was fascinating because it ties together important issues in healthcare and environmental studies. Many environmental groups have been advocating for a reduction in meat consumption for a variety of reasons centered largely around reducing environmental degradation; however, this study and others like it could provide additional support for eating less in meat in our diets, and perhaps, since it involves direct consequences on human health, people might be more willing to listen.

  4. It had not occurred to me until now that there is widespread use of antibiotics on agricultural animals in the meat industry. I agree with Courtney's comment that this is another valuable environmental reason to reduce meat consumption. Perhaps this will especially encourage people to reduce their meat consumption because this consequence has the potential to directly affect them.