title: Mutation in DNA gyrase of norfloxacin-resistant clinical isolates of Neisseria gonorrhoeae.
abstract: OBJECTIVE
  Recently a rapid decrease in the susceptibility of Neisseria gonorrhoeae isolates to fluoroquinolones has occurred and gonococcal fluoroquinolone resistance is now a significant problem in the treatment of gonorrhoea in Japan. Thus, in order to investigate the quinolone resistance mechanisms in clinical isolates of N gonorrhoeae we studied an alteration in the DNA gyrase subunit A (GyrA) which is well-known as a common mechanism of bacterial quinolone resistance.
  
  
  METHODS
  Four clinical isolates of N gonorrhoeae resistant to norfloxacin and 5 strains susceptible to norfloxacin, including 2 clinical isolates and 3 WHO reference strains, were tested in this study. To identify mutations in the GyrA genes of gonococcal strains, polymerase chain reaction and direct DNA sequencing were performed.
  
  
  RESULTS
  A single base change (serine codon TCC changed to phenylalanine codon TTC), which resulted in an amino acid change in GyrA at position 91, was identified in all 4 norfloxacin-resistant strains for which the MICs of norfloxacin ranged from 1.0 to 8.0 micrograms/ml, while no mutation within GyrA was detected in 5 norfloxacin-susceptible strains for which the MICs of norfloxacin ranged from 0.004 to 0.063 microgram/ml.
  
  
  CONCLUSIONS
  The results from this study suggest that the serine-91 to phenylalanine substitution in GyrA is probably an essential mutation in fluoroquinolone resistance in clinical isolates of N gonorrhoeae.
authors.affiliation: Department of Urology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Tanaka
authors.forename: M
authors.initials: M
authors.lastname: Otsuki
authors.forename: T
authors.initials: T
authors.lastname: Nishino
authors.forename: I
authors.initials: I
authors.lastname: Kobayashi
authors.forename: T
authors.initials: T
authors.lastname: Matsumoto
authors.forename: J
authors.initials: J
authors.lastname: Kumazawa
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004352:Drug Resistance, Microbial; D008826:Microbial Sensitivity Tests; D009344:Neisseria gonorrhoeae / Q000201:enzymology / Q000235:genetics*; D009643:Norfloxacin / Q000494:pharmacology*; D017354:Point Mutation
chemical_list: D000890:Anti-Infective Agents; D004250:DNA Topoisomerases, Type II; D009643:Norfloxacin