Ominous drug-resistance hints appear. (Biomedicine).

Haemophilus influenzae, a bacterium that's a common cause of pneumonia and meningitis, has developed signs that it may be on a path toward resistance to an important line of antibiotics, scientists report.

The drugs, called fluoroquinolones, include ciprofloxacin, now famous for its role in fighting anthrax. The antibiotics are often physicians' last resort against H. influenzae infections, severe cases of which can land people in the hospital. H. influenzae is a leading cause of deaths from respiratory infections.

H. influenzae isn't related to the influenza virus but can occur as a secondary infection in people who have the flu.

While other microbes, such as those causing gonorrhea, have shown resistance to fluoroquinolones, the new findings represent the first sign of future resistance by H. influenzae, says Stuart B. Levy of Tufts University Medical School in Boston. He and his colleagues found H. influenzae cells with gene mutations that turn up in other drug resistant microbes.

The researchers report that 3 years ago, blood samples from people in North America and Europe infected with H. influenzae revealed fewer than 1 bacterium per 1,000 with these worrisome genetic traits. This year, that rate has increased to between 1 and 2 such bacteria per 1,000. While still small, such numbers suggest the bacterium is progressing toward resistance, says Levy.

"We can learn something by tracking resistance in an organism over time," Levy says. He and his colleagues are now working with drug companies in a collaboration called the Alliance for the Prudent Use of Antibiotics to spot signs of drug resistance in various bacteria. "We're going to need some sort of early warning system, and this surveillance [program] seems to be the best bet," he says.

Despite the hints of resistance shown by H. influenzae, fluoroquinolones still work against infections. But only appropriate, discriminating use of the drug will keep the bacterium from becoming fully resistant to the antibiotic, Levy says. Patients should take all of a given dose to minimize the development of resistant microbes and use fluoroquinolones only when they're truly needed, he says. --N.S.