The researchers sampled feedlot dust in the air upwind and downwind of the cattle farms.
Image credit: Brett Blackwell/TTU.
A team from the Institute of Environmental and Human Health at Texas Tech University (TTU) in Lubbock, TX, analyzed air samples around feedlots at cattle farms in the Southern High Plains that lie in northwestern Texas.
In the journal Environmental Health Perspectives, they report how they found evidence of feedlot-derived bacteria, antibiotics and bits of DNA that code for antibiotic resistance, in the samples.
The study is thought to be the first to document evidence of airborne transmission of antibiotic resistance from an open-air farm setting.
The researchers accept that while they couldn't assess whether the amounts of the materials they found were dangerous to humans, the results shed light on previously unanswered questions about which routes antibiotic-resistant bacteria could be using to travel long distances to places inhabited by humans.
70% of antibiotics are used in animal farming
Senior author Phil Smith, an associate professor of terrestrial ecotoxicology at TTU, says we are all fairly sure that antibiotic resistance comes from extensive use of antibiotics in animal farming, where around 70% of all antibiotics are used.
He says we also know bacteria are very "promiscuous" about swapping and sharing their genetic material, which crosses easily into other species. So we know the mechanism through which resistance develops. But what we don't know so much about is how the resistant bacteria travel and move in the environment, says Prof. Smith.
In an attempt to address some of the questions surrounding this mystery, the team analyzed air samples taken upwind and downwind of each feedlot.
Feedlots appear to be the source of airborne antibiotic resistance
The analysis showed there were more bacteria, antibiotics and DNA sequences that code for antibiotic resistance in the downwind than the upwind air samples, pointing to the feedlots as the source.
Bacteria are quite resilient beings and can survive on the particulate matter of the feedlot dust as they travel in the wind. And because the antibiotics travel with them, this puts them under selective pressure to retain their resistance as they multiply - the non-resistant ones just don't finish the journey.
As the wind blows across the Southern High Plains, it carries with it the particulate matter with its burden of antibiotics and bacteria. The particles travel far from their starting point at the feedlot.
Coupled with the dust storms that frequent West Texas, you have a plausible route through which antibiotic resistance can spread across hundreds of miles into cities and towns, and perhaps even around the world.
Co-author Greg Mayer, an associate professor of molecular toxicology at TTU, says:
"I think implications for the spread of some feedlot-derived, antibiotic-resistant bacteria into urban areas is paramount to the research."
He explains that while they haven't yet sampled particulate matter in urban areas to see if they contain bacteria from the feedlots, or whether they still contain antibiotic resistant bacteria, he believes the study is "proof of principle" for an airborne pathway for the spread of antibiotic resistance.
Prof. Mayer says further studies should now be done to see where the particulate matter from the feedlots travels to and "what is happening to its passengers when it gets there."
The study follows a recent Review on Antimicrobial Resistance commissioned by British Prime Minister David Cameron that found the failure to deal with drug-resistant infections and their causes could lead to 10 million extra deaths per year by 2050. The associated global cost of such a devastating loss would be $100 trillion.
Meanwhile, Medical News Today recently learned about a study that found travelers may be helping the spread of superbugs by taking antibiotics for diarrhea, an illness frequently experienced when they go on trips.