DEVELOPMENT OF FLUOROQUINOLONE RESISTANCE AND MUTATIONS INVOLVING GYRA AND PARC PROTEINS AMONG NEISSERIA-GONORRHOEAE ISOLATES IN JAPAN

Purpose: To investigate the development of fluoroquinolone resistance among Neisseria gonorrhoeae isolates in Japan and the frequency and pa tterns of mutations involving the GyrA and ParC proteins, which confer quinolone resistance to the bacteria, in isolates. Materials and Meth ods: Antimicrobial susceptibilities of 145 gonococcal isolates, includ ing 79 isolated from February 1992 through February 1993 and 66 isolat ed from February 1995 through February 1996, to six fluoroquinolones a nd several other antibiotics were compared with those of 27 isolates o btained from 1981 through 1984. To identify mutations in gyrA and parC genes of the isolates, the quinolone resistance-determining regions o f the gyrA and parC genes were PCR-amplified and the PCR products were directly sequenced. Results: The minimum inhibitory concentration for 90% of strains (MIC90) values of norfloxacin for the isolates from 19 92 to 93 (4 mu g./ml.) and 1995 to 96 (8 mu g./ml.) were 16- and 32-fo ld, respectively, higher than those for isolates from 1981 to 84 (0.25 mu g./ml.). The MIC90 values of ciprofloxacin for isolates from 1992 to 93 (0.5 mu g./ml.) and 1995 to 96 (1 mu g./ml.) showed increase of 8- and 16-fold, respectively, in comparison with those from 1981 to 84 (0.063 mu g./ml.). The isolates from 1992 to 93 and 1995 to 96 were a lso less susceptible to newer fluoroquinolones including levofloxacin, sparfloxacin, DU-6859a and AM-1155, as compared with those from 1981 to 84. In 46 (67.6%) and 16 (23.5%) of the 68 gonococcal strains seque nced, GyrA and ParC mutations were identified, respectively. No ParC s ubstitutions were identified in any isolates without co-existence of t he GyrA mutation. A Ser-91 to Phe mutation, which was detected in 30 ( 65.2%) of the 46 isolates with GyrA mutations, was the most common Gyr A mutation. Mutants with the single Ser-91 to Phe substitution in GyrA were 12-fold and at least 13-fold, respectively, less susceptible to norfloxacin and ciprofloxacin than the wild type. Conclusions: The res ults obtained in this study suggest that a high prevalence of gonococc al isolates with the Ser-91 to Phe mutation in GyrA has reduced the su sceptibility of this organism to fluoroquinolones in Japan.