NEW NORFLOXACIN RESISTANCE GENE IN PSEUDOMONAS-AERUGINOSA PAO

A new type of norfloxacin-resistant mutant of Pseudomonas aeruginosa PAO was isolated. This mutant showed cross resistance to imipenem and chloramphenicol and hypersusceptibility to β-lactam and aminoglycoside antibodies. The new norfloxacin resistance gene nfxC was mapped near catA (46 min) on the PAO chromosome. Norfloxacin accumulation was decreased in the nfxC mutant; furthermore, the rate of imipenem diffusion through the outer membrane of the nfxC mutant was lower than that of the parent strain. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of outer membrane proteins showed a decrease of a 46-kilodalton protein and an increase of a 50-kilodalton in the nfxC mutant. We conclude that nfxC is a new norfloxacin resistance gene that affects outer membrane permeability to quinolones and other antimicrobial agents.