Amid bleak outlook, antibiotic shines.

Research on a novel antibiotic offers a rare dose of optimism as existing microbe-killing compounds are losing effectiveness and the pipeline of new antibiotics is drying up.

Injections of the compound called PTK 0796 kept mice alive after they had been infected with otherwise lethal doses of Streptococcus pneumoniae, the inventors' of the drug report. In one experiment, all mice treated with at least 0.5 milligrams of the drug per kilogram of bodyweight survived infection. By comparison, only half of animals treated with similar concentrations of another antibiotic, minocycline, survived infection, say S. Ken Tanaka and his colleagues at Boston-based Paratek Pharmaceuticals.

In another experiment with a strain of S. pneumoniae that's resistant to several antibiotics, mice could be saved with 1 mg/kg of PTK 0796. Other mice died with even 50 mg/kg of minocycline.

In other studies, the researchers found that their compound is active against a broad spectrum of human pathogens.

Paratek Pharmaceuticals has allied itself with the pharmaceutical giant Bayer to further develop PTK 0796, which belongs to a distinct new class of antibiotics derived from tetracycline.

Apart from Paratek's new agent, there are few promising antibiotics in early stages of development, says Steven J. Projan of Wyeth Research in Cambridge, Mass. Wyeth is currently testing another new tetracycline-like antibiotic, called tigecycline, but several other major companies recently curtailed research and development of new antibiotics, Projan notes.--B.H.