Study Says Antibiotic-Resitant E. coli Can Pass From Animals to Humans
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Reviewed By Laura J. Martin, MD
May 18, 2010 -- Hong Kong researchers have found that antibiotic resistance to E. coli is found in both humans and animals, signifying that these resistant bacteria may be transmitted from animals to humans.
The research is published in the Journal of Medical Microbiology.
The study shows the genes that cause bacteria to be resistant to a common antibiotic can be transferred between people and animals, says study researcher Pak-Leung Ho, MD, a researcher at the Carol Yu Centre for Infection at the University of Hong Kong.
The gene, aacC2, was initially sequenced around the mid-1980s, Ho tells WebMD. "Initially, we found that these genes were common among urine isolates from outpatients with urinary tract infections," he tells WebMD. The gene encodes resistance to gentamicin, an antibiotic.
Next, says Ho, his research team decided to collect bacterial strains from people and animals "to address the question that these genes could have come from food animals."
The researchers gathered 249 samples of E. coli, which is responsible for up to 95% of urinary tract infections in people, Ho says.
Of these, 89 were found to be gentamicin-sensitive (60 from people, 29 from animals) and 160 gentamicin-resistant (107 from people, 53 from animals).
In all, 84.1% of the resistant samples from people and 75.5% from animals were found to have the aacC2 gene, Ho's team found.
Next, they sequenced the gene for 10 animal and 10 human samples. They found that two alleles, alternative forms of a gene, were equally distributed in the people and animal samples.
The gene was found on DNA sections known to swap between different bacterial populations, Ho found. That suggests to the researchers that the aacC2 can transfer between separate bacterial populations that affect animals and people.
The bottom line? "Consumers may acquire antibiotic-resistant bacteria from contaminated food," Ho says.
"Good personal and food hygiene are the best ways to prevent this."
The findings also suggest that "regulatory agencies should partner with researchers and industry to conduct more quantitative assessments such as the one reported by us," Ho says.
The problem may be worse in developing countries, he says, where little is known about the type and amount of antibiotics used in producing food animals.
The new report should not be cause for undue alarm, says Roger Clemens, DrPH, adjunct professor of pharmacology and pharmaceutical sciences at the University of Southern California, Los Angeles, and a spokesman for the Institute of Food Technologists.
He puts the problem in perspective. "Just because you have resistance doesn't mean all bacteria in the [urinary] tract are resistant," he says, noting that the body has a balance of friendly and unfriendly bacteria.
The new report is a reminder, however, that food safety is a critical issue, he says. "It adds more fuel to say we need to be more diligent about food safety," he tells WebMD.
"Bacteria are talking to bacteria," he says of the Ho findings. "We need to keep that microbe world under control. This has been a concern for decades within the medical community."
In the U.S., proposed legislation would help limit the use of antibiotics in animal agriculture, which some experts say are overused and too often given for non-therapeutic purposes, such as to promote faster growth.
Called the Preservation of Antibiotics for Medical Treatment Act, the proposed legislation would require that the FDA conduct another review of approvals already issued for animal-feed use of antibiotics important for human medicine and rescind the approvals of any found to be unsafe when it comes to resistance.
Women are more prone than men are to urinary tract infections, and the rate of the infections increases in women as they age. Those with diabetes are also more likely to get UTIs due to immune system changes.
UTIs account for more than 8 million doctor visits a year, according to the National Institutes of Health.
Symptoms may include an urge to urinate and a painful burning sensation during urination.
Treatment is with antibacterial drugs, but antibiotic resistance is an increasing problem.
SOURCES: Pak-Leung Ho, MD, department of microbiology, Carol Yu Centre for Infection, University of Hong Kong.
Ho, P. Journal of Medical Microbiology, June 2010.
Roger Clemens, DrPH, adjunct professor of pharmacology and pharmaceutical sciences, department of pharmacy, University of Southern California, Los Angeles; spokesman, Institute of Food Technologists.
Preservation of Antibiotics for Medical Treatment Act of 2009.
National Institutes of Health: "Urinary Tract Infections in Adults."
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