Antibiotic use in food animals may cause human drug resistance

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.

Campylobacter jejuni is a leading bacterial cause of foodborne illness in industrialised 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 the antibiotic 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 industrialised nations, but it has avoided using the antibiotics that have been standard in the other countries' food animal production.

To evaluate whether the antibiotic policy has affected bacterial drug resistance, 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% 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%.

"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 industrialised nations have also realised the apparent benefits of restricting antimicrobial use in animals. Sweden prohibited the use of fluoroquinolones for food animals in 1986, Norway has never allowed their use in food animals, and both countries have also reported low trends, in fluoroquinolone-resistant Campylobacter infecting humans.