Animal Farms May Produce Superbugs

Flies, Roaches on Pig Farms May Spread Antibiotic-Resistant Bacteria to Humans

Medically Reviewed by Laura J. Martin, MD on January 25, 2011

Jan. 25, 2011-- Superbugs that are resistant to antibiotics, long known to create life-threatening infections in hospital patients, could also be originating from animal farms where antibiotics are used to promote growth, potentially threatening human health, new research suggests.

It's not the pigs causing the potential problem, but rather the insects commonly found on these pig farms, including flies and cockroaches, says Ludek Zurek, PhD, an associate professor of microbial ecology at Kansas State University, who led the study.

The insects were found to have many of the same antibiotic-resistant bacteria in their guts as did the swine and therefore could be responsible for spreading the antibiotic-resistant bacteria to people, once they travel from the farms, he tells WebMD.

"These insects are more than just a nuisance, which is how they are viewed on the farms," he says. "They could represent a potential risk of spreading bacteria from pig manure [to] outside farms."

The flies, he says, can travel from the farms to surrounding residential areas. "Workers can carry the cockroaches accidentally [from the farm] with them to their houses and establish cockroach populations wherever those people live." Once in a home, the insects can potentially contaminate food and drink with the resistant bacterial strains, Zurek says.

The study is published in BMC Microbiology.

Superbugs From the Farm: Study Details

Zurek's team visited several swine farms in North Carolina and Kansas, collecting the insects and fecal matter from the pigs. Back in the lab, they isolated bacteria from the pig feces, comparing them to the bacteria present in the intestines of the house flies and cockroaches.

''We saw that there is a very good match between bacteria we got from the pigs and houseflies and cockroaches," he tells WebMD.

The researchers focused on two common gut bacteria, Enterococcus faecalis and Enterococcus faecium, analyzing 119 samples from pigs, 83 from cockroaches, and 162 from flies.

Enterococci were found in nearly 90% of the pig samples, 94% of the cockroach samples, and more than 98% of the fly samples.

"We tested these [samples] for antibiotic resistance against eight different antibiotics used in human medicine, and some in animal medicine," Zurek tells WebMD.

And they found the antibiotic resistance profile was very similar between the pigs and the insects.

Samples from all were found to be highly resistant to tetracycline. They were also found resistant to erythromycin, streptomycin, and kanamycin.

The study was funded by the U.S. Department of Agriculture.

Superbugs From Farms: Implications

While there are no direct studies to show the link between bacteria in insects found on pig farms and human health, according to Zurek, he says the potential risk is there.

The best strategy for operators of swine farms? Zurek says the operators should try to lower the population of the insects, both flies and cockroaches. "It's impossible to get rid of them," he says.

Superbugs From Farms: Other Views

The new research echoes those of other studies, says Abigail Salyers, PhD, professor of microbiology at the University of Illinois-Urbana, who reviewed the study for WebMD.

The concern among scientists, she says, is that once your intestinal tract becomes colonized with these bacteria, "you are like a ticking time bomb."

Later, if you get an infection following a procedure in the abdominal cavity, such as an appendix removal or a colonoscopy that accidentally perforates the colon, the worry is that the antibiotic-resistant bacteria can make treatment difficult.

"This is a theoretical concern," she tells WebMD. "There's so much talk about whether there is a risk or not, we need to do the study to find out is there a risk to human health or not [from these organisms]," she says."There is a potential problem here but it hasn't been proven."

Speaking on behalf of the National Pork Board, Paul Sundberg, DVM, PHD, tells WebMD that his organization welcomes scientifically based information and research.

However, he says, "Saying something that happens out on the farm affects something in the city is conjecture."

"Enterococci is a ubiquitous organism," he says. It would have been big news, he says, if the samples hadn't contained it.

''No one is going to say enterococci couldn't multiply on a piece of food that could have come from flies. It's within possibility, but the question is, how biologically plausible and feasible is this as a risk to human health?"

Show Sources


Ludek Zurek, PhD, associate professor of microbial ecology, Kansas State University, Manhattan.

Ahmad, A. BMC Microbiology, Jan. 25, 2011.

Paul Sundberg, DVM, PhD, vice president, science and technology, National Pork Board, Des Moines, Iowa.

Abigail Salyers, PhD, professor of microbiology, University of Illinois-Urbana.

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