By Julie Steenhuysen

CHICAGO, July 15 (Reuters) - Treatment with a common malaria drug may explain why people in remote villages in South America have high levels of resistance to a widely used class of antibiotics known as fluoroquinolones, despite never having taken the drugs, Canadian researchers said on Tuesday.

The surprising findings suggest that treating malaria with the cheap, widely used drug chloroquine -- a close cousin of fluoroquinolones -- may boost the risk of resistance to these antibiotics, they said.

Fluoroquinolones or quinolones are among the most commonly used antibiotics in North America and Europe, said Dr. Michael Silverman of Lakeridge Health Centre in Oshawa, Ontario. "Loss of these drugs would be a major blow to public health," said Silverman, whose study appears in the journal PLoS One.

He and colleagues studied people in extremely remote villages in the Guyanese rain forest during humanitarian medical visits between 2002 and 2005.

Silverman said this population had never been exposed to fluoroquinolones, and thus represented a unique population to study antibiotic resistance, which is thought to be linked with the overuse of antibiotics. He had expected to find none.

Instead, they found 4.8 percent of people studied had strains of E. coli that were resistant to the antibiotic ciprofloxacin, the generic name for Bayer AG's <BAYG.DE> drug Cipro, and one of the most popular fluoroquinolones.

Silverman said a resistance rate of 4.8 percent is especially high considering that a 2003 study published in the Journal of the American Medical Association found a 4 percent resistance rate in intensive care units in North America, where the drug is widely used.

Tests of local water samples confirmed that no antibacterial agents were found in the drinking water, but chloroquine, used to fight malaria, was present.

OTHER DRUGS COULD BE AFFECTED

To confirm that chloroquine could cause resistance, the researchers combined the drug with bacteria in the lab and found that it had a weak antibiotic effect. It was not enough to kill the bacteria, but enough to develop resistance.

Silverman said resistance to Cipro could extend to newer drugs in the class such as Johnson & Johnson's <JNJ.N> Levaquin or levofloxacin and Bayer's Avelox or moxifloxacin.

"We tested for Cipro because that is still the most widely used, but we know any bacteria that is resistant to one is resistant to all," Silverman said.

He said the findings could have implications for a new generation of malaria therapies known as artemisinin-based combination therapies, or ACT drugs, which are recommended by the World Health Organization because of growing resistance to older treatments such as chloroquine.

ACT therapies usually include quinoline drugs similar to chloroquine, Silverman said. "The question is, 'Is this true of all quinolines or just chloroquine?'"

Silverman said the findings help explain high rates of resistance to fluoroquinolones in tropical regions.

"What we have to do is redouble our efforts to prevent malaria, so we can use less of these drugs," he said.

Malaria, caused by a parasite carried by mosquitoes, kills more than 1 million people a year worldwide. The full study can be found at http://www.plosone.org/doi/pone.0002727.

(Editing by Will Dunham)

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