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Less antibiotic use in food animals leads to less drug resistance in people, study shows

April 18, 2006

Australia's policy of restricting antibiotic use in food-producing animals may be linked with lower levels of drug-resistant bacteria found in its citizens, according to an article in the May 15 issue of Clinical Infectious Diseases, now available online.

Campylobacter jejuni is a leading bacterial cause of foodborne illness in industrialized countries. Drug resistance can make Campylobacter infections difficult for physicians to treat, and can result in longer bouts of diarrhea and a higher risk of serious or even fatal illness. Bacterial resistance to drugs is generally attributed to inappropriate prescribing or overuse of antibiotics.

An Australian solution to the drug resistance problem has been to prohibit the use of certain antibiotics, called fluoroquinolones, in food animals such as poultry. Such a policy puts Australia in a relatively unique position, since its animal and food production levels are comparable to those of other industrialized nations, but it has avoided using the antibiotics that have been standard in the other countries' food animal production.

To evaluate whether the country's restrictive antibiotic policy has affected bacterial drug resistance, Australian researchers examined C. jejuni isolates collected from 585 patients in five Australian states. None of the patients had received fluoroquinolone treatment within the month prior to becoming ill. The researchers discovered that only 2 percent of the locally acquired Campylobacter isolates were resistant to ciprofloxacin, a type of fluoroquinolone. Countries that allow fluoroquinolone use in animals may have a drug resistance prevalence of up to 29 percent. Ciprofloxacin can be used to treat severe Campylobacter disease, so a low level of bacterial drug resistance should lead to better treatment efficacy.

"There are different causes that lead to bacterial antibiotic resistance, and use of antibiotics in food animals is only one of the multiple causes," said lead author Leanne Unicomb, an epidemiologist with OzFoodNet and Australia National University. However, the evidence indicates that "use of fluoroquinolones in food animals in other countries has increased the risk of resistance in [Campylobacter] isolates infecting humans," she said. The researchers concluded that the low drug resistance they found "probably reflects Australia's policy of prohibiting fluoroquinolones for animal use."

Other industrialized nations have also realized the apparent benefits of restricting antimicrobial use in animals. Sweden prohibited the use of fluoroquinolones for food animals in 1986, Norway has never licensed their use in food animals, and both countries have reported low trends-similar to Australia's-in fluoroquinolone-resistant Campylobacter infecting humans. The United States, in a recent effort to reduce American levels of Campylobacter drug resistance, has taken a cue from other countries' success. The U.S. Food and Drug Administration proposed banning fluoroquinolones in poultry in 2000, but one drugmaker fought the ban until it was finally enacted in September 2005.

Reducing the use of antibiotics in food animals, coupled with the authors' additional recommendation of "sensible use of fluoroquinolones in clinical settings," seem to be steps in the right direction toward curbing harmful foodborne bacterial drug resistance.

Infectious Diseases Society of America