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Antibiotic Resistance Takes Form on the Farm

Drug-resistant genes traced from animals to groundwater

WEDNESDAY, May 23, 2001 (HealthDayNews) -- One reason antibiotics are losing the power to fight human diseases may be found down on the farm, says a new study.

Researchers at the University of Illinois at Urbana-Champaign have traced antibiotic-resistant genes from pig farms to groundwater, suggesting that resistance is being built up through the food chain. The discovery raises concerns because antibiotics are widely used to fatten livestock and prevent disease in the animals in the United States.

"The genes are found in bacteria, and the tetracycline-resistant genes in the bacteria travel into the groundwater, where the horizontal transfer of the genes occur," says lead study author Rustam I. Aminov, a microbiologist and visiting professor of animal science.

"The resistant genes get into the ground and drinking water and will find their way into the guts of people, animals and wildlife, passing on the resistance in a continuous gene cycle," he says.

The research team analyzed water samples from lagoons, wells and groundwater on and near two Illinois pig farms, and through a DNA-amplification technique, identified the trail taken by the resistant genes.

The amplification process, called a polymerase chain reaction (PCR), rapidly duplicates DNA, allowing experts to identify a gene's unique fingerprint.

"These [antibiotic resistant] genes were found to be predominant in the gastrointestinal tracts of pigs and steers" and suggested the flow of the genes to the water came directly from the animals, say researchers.

"This work is still in its infancy," and it's too early to draw any conclusions based on this study, says Kammy Johnson, an epidemiologist with the National Center for Environmental Health at the Centers for Disease Control and Prevention. "But it's exciting to see the technology that's being developed to look at this problem."

With PCR, it "may be plausible to fill in all of those blanks in those basic questions. It's changed the way we think of infectious processes and is going to have great promise … to track pathogens throughout the environment," Johnson says.

Aminov says the process by which antibiotic resistance may be passed along "is really poorly understood." In another investigation, he says researchers are looking at the disposal of livestock waste products, which may be returned to the ground in forms of manure.

From there, antibiotic resistance may transfer to corn or soybeans, as either livestock feed or consumer product, says Aminov.

He says antibiotics to make farm animals bigger has been banned in Sweden since the l980s, and the European Union is currently phasing out the practice.

Aminov says 21 antibiotics now are "administered to swine for growth promotion or prophylaxis, and we studied only one class of the gene. He says the problem is of particular concern in rural areas where people use untreated well water, which they assume is very clean.

"There is a race for profit because agricultural [work] is so low profit, and many depend on antibiotics to survive," but using antibiotics to fatten animals or prevent disease may make the drugs useless in fighting human disease, he says.

"We have to preserve antibiotics for other purposes," says Aminov.

The study is published in last month's issue of Applied and Environmental Microbiology.

What To Do:

The antibiotic resistance project at the Centers for Science in the Public Interest has tips for using antibiotics.

Check groundwater contaminants to learn more about the problem.

For more HealthDay stories on antibiotics click here.

SOURCES: Interviews with Rustam I. Aminov, Ph.D., microbiologist, visiting professor of animal science, the University of Illinois at Urbana-Champaign; Kammy Johnson, D.V.M., Ph.D., epidemiologist, National Center for Environmental Health, Centers for Disease Control and Prevention; April 2001 Applied and Environmental Microbiology
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