RAPID DECLINE IN PENICILLINASE-PRODUCING NEISSERIA-GONORRHOEAE IN HONG-KONG ASSOCIATED WITH EMERGING 4-FLUOROQUINOLONE RESISTANCE

Objective-To study the changes in penicillinase-producing (PPNG) and h igh-level tetracycline resistant (TRNG) Neisseria gonorrhoeae isolated in Dong Kong associated with emerging quinolone resistance (QRNG) ove r a two year period from November 1992 to October 1994. Materials and methods Four thousand and eighty-six strains of Neisseria gonorrhoeae isolated, of which 432 were PPNG, were examined for susceptibilities t o penicillin and tetracycline by an agar dilution method using the bre akpoint minimum inhibitory concentrations (MICs) of 1 and 10 mg/l resp ectively. Ofloxacin susceptibility was done using 0.1 and 1 mg/l. Peni cillinase production was detected by performing the chromogenic cephal osporin nitrocefin test on all penicillin resistant (MIG > 1 mg/l) str ains. Results-Three thousand and eighty (75.4%) and 79 (1.9%) strains were found to be penicillin resistant and TRNG (MIC > 10 mg/l) respect ively. Sixty-nine strains (1.7%) were resistant to both, of which 54 ( 1.3%) were PPNG. Three strains were multiply-resistant to penicillin, tetracycline and ofloxacin; however, none was PPNG. While the percenta ge of penicillin resistant strains remained stable (mean 75.5%, SD 7.0 ), TRNG decreased from 4.5% to 2.1%. The most dramatic change was the sharp decline of PPNG from 25.5% in January 1993 to 4.3% in October 19 94, concurrent with a linear increase in strains with ofloxacin MIC > 0 1 mg/l. Significant clinical failure was seen in strains having oflo xacin MIC > 1 mg/l (QRNG), which increased drastically from 0.5% to 10 .4% during the study period. Selection against PPNG and TRNG strains a ppeared to occur only when fully quinolone-susceptible strains first b ecome less susceptible (MIG > 0 1 mg/l), but not when these less susce ptible strains become fully resistant (MIG > 1 mg/l). Conclusion-PPNG is now no longer hyperendemic in Hong Kong. Emergence of QRNG is assoc iated with rapid decline of both PPNG and TRNG. This is the first repo rt of plasmid-curing effect of the 4-fluoroquinolones occurring on an ecological scale.