By Julie Steenhuysen Wed Jul 16, 1:54 AM ET

CHICAGO (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 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 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.