Use of antibiotics in cattle feed leads to airborne antibiotic-resistant bacteria – study

Reuters/Darren Hauck

Reuters/Darren Hauck

DNA from antibiotic-resistant bacteria is spreading from cattle feedlots across the US through the air, a new study has found. The report indicates that so-called superbugs threatening humans could be traced to the use of antibiotics in cattle feed.

Antibiotic-resistant bacterial DNA is known to be transferable to
humans if ingested via water or meat. The authors of the study
sought to determine the extent to which antibiotics,
antibiotic-resistance genes and microbes associated with
ruminants like cattle are dispersed into the air via particulate
matter derived from large scale beef cattle feedyards, they

wrote in their abstract
. The paper is set to be published in

Despite evidence that agricultural use of antibiotics is a
contributor to antibiotic-resistance, animal agriculture uses
nearly 10 million kg of antibiotics annually in the United States

“This is the first test to open our eyes to the fact that we
could be breathing these things,”
Phil Smith, one of the
paper’s authors and an environmental toxicologist at Texas Tech
University, told the Texas Tribune.

READ MORE: Superbugs could kill 10mn per year by
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The scientists looked at the more than three-quarters of all
cattle on US feedyards with more than 1,000 head ‒ a total of
8.24 million cattle ‒ were located in Texas, Oklahoma, Kansas,
Nebraska and Colorado, an area called the Southern High Plains
that “has the highest frequency of dust storms in the United
States and the highest density of feedyards,”
the authors

“Feedyard pen floor material, which consists primarily of
urine and fecal material, becomes dry and brittle, thus becoming
source material for fugitive dust” f
rom the feedyards in the
region, the researchers wrote. “Thus, in semi-arid regions
where a majority of beef cattle feedyards exist in North America,
transport of livestock-generated organic wastes occurs largely
via wind.”

Between August and December 2012, the researchers collected
particulate matter samples in air filters from areas next to ten
commercial beef cattle feedyards in the Southern High Plains.
They measured the air both upwind and downwind of the ten
locations for half an hour in the afternoons “when cattle are
most active and the greatest amount of [particulate matter] is
They then extracted the DNA from the particulate
matter bound to the air filters, in which they detected the
presence of nine antibiotic resistant genes.

The scientists also measured whether there were differences
between the upwind and downwind particulate matter, and they
found that the downwind air contained antibiotics, bacteria, and
a much greater number of microbial communities containing
antibiotic-resistant genes than the upwind air.

They noted that three tetracycline antibiotics (tetracycline,
chlortetracycline, and oxytetracycline) were detected together in
the majority of particulate matter samples downwind of feedyards
(60 percent), while oxytetracycline was the most frequently
detected of the three antibiotics, and it was detected in 100
percent of the samples collected downwind of feedyards and 30
percent of upwind samples.

“The ‘aha’ moment came when we saw how much more prevalent
resistant sequences were downwind than upwind,”
Greg Mayer,
a molecular biologist at Texas Tech and one of the study’s
authors, told the Texas Tribune. “It was not just higher in
some of them – it was 4,000 percent more. It made me not want to

The authors noted their concern in their paper.

“This study clearly demonstrates the potential for
antibiotics and bacteria to be transported from beef cattle
feedyards into the environment by wind. Thus, it is reasonable to
consider how far microbes may be transported from these sources,
and if they remain viable after aerial transport,”
researchers wrote. “This study was not designed to address
these questions directly, rather it was intended to quantify
airborne antibiotics, changes in microbial community composition,
and identify antibiotic resistance genes derived from a potential

READ MORE: Antibiotics ‘fail 15%’ of patients due
to superbugs and ‘reckless’ prescription

“While many of the veterinary antibiotics approved for use in
beef cattle production are not intended for human use, the
potential for resistance to multiple antibiotics within the same
class or otherwise, including those intended for human use, has
been documented,”
they added.

The cattle industry is pushing back against the study, saying it
misrepresents the risk of super bacteria to human health, and
deems its findings partial and inconclusive. Dr. Sam Ives, a
veterinarian working with the Texas Cattle Feeders Association,
told the Texas Tribune that antibiotic use in the industry is

“If I truly thought that the usage of these products was
putting anyone at danger, I wouldn’t be using them,”
said. “My children work with me in the feedlot; my wife works
with me. Am I concerned for their safety? No, I’m not.”

But physicians may be taking the researchers’ side. In 10 years
of treating patients at his Lubbock clinic, Dr. Randall Wolcott
told the Texas Tribune that he has seen bacteria grow
increasingly resistant to antibiotics used to treat their

“We know that antibiotic-resistant genes are becoming more
Wolcott said. “We use too many antibiotics for
animal health, and it keeps food prices down. Is it a good
tradeoff? This research is a piece of the puzzle that will help
decide that question.”

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