Characterization of sparfloxacin-resistant mutants of Staphylococcus aureus obtained in vitro

A sparfloxacin-susceptible clinical isolate of Staphylococcus aureus was gr own in increased concentrations of sparfoxacin. The presence of mutations i n gyrA, gyrB, grlA and grlB genes was analyzed. The primary point mutation was located in the gyrA gene (Glu-88 to Lys). Two further mutation steps ap peared in the amino acid change Ser-80 to Tyr in GrlA. No mutations occurre d in the gyrB or grlB genes. Efflux pumps involved in the increase of resis tance were also found to affect norfloxacin and ciprofloxacin. This effect may be related to NorA. An overexpression of NorA, may be associated with t he increase of the MIC of norfloxacin from 32 mg/l to > 200 mg/l in the fin al mutant. The MICs levels of sparfloxacin were affected by unknown mechani sm. (C) 2001 Elsevier Science B.V. and International Society of Chemotherap y. All rights reserved.