IN VITRO SELECTION OF FLUOROQUINOLONE-RESISTANT NEISSERIA GONORRHOEAE HARBORING ALTERATIONS IN DNA GYRASE AND TOPOISOMERASE IV

Purpose: We attempted to select increasingly fluoroquinolone-resistant strains of Neisseria gonorrhoeae in vitro and to assess whether selected mutants harbored alterations in the GyrA subunit of DNA gyrase and the ParC subunit of DNA topoisomerase IV, which were analogous to those in fluoroquinolone-resistant clinical isolates.Materials and Methods: A fluoroquinolone-susceptible strain was exposed to norfloxacin in vitro. Selected mutants were sequentially exposed to norfloxacin, and this procedure was repeated. For 11 mutants, minimum inhibitory concentrations (MICs) of antimicrobial agents were determined, and mutations in the region corresponding to the quinolone resistance-determining region (QRDR) of the Escherichia coli gyrA gene and the analogous region of the parC gene were analyzed.Results: Mutants obtained in one step exhibited significantly increased MICs of norfloxacin, ofloxacin and ciprofloxacin and had a single amino acid change in GyrA. Two-step mutants exhibited significantly higher norf...