COMPARISON OF E-TEST WITH AGAR DILUTION METHODS IN TESTING SUSCEPTIBILITY OF N-GONORRHEA TO AZITHROMYCIN

Background and Objectives: The antimicrobial susceptibility pattern of Neisseria gonorrhoeae varies from one country to another and may also change with time, To monitor these variations and changes, it is desi rable to have a method that is simple and reproducible, This study was undertaken to determine the in vitro susceptibility of N, gonorrhoeae to azithromycin and to assess the reliability of results obtained usi ng E-test methodology for determination of the minimum inhibitory conc entration (MIC) of azithromycin, Study Design: The MICs for 135 clinic al isolates of N, gonorrhoeae were determined by a modified Kirby-Baue r method recommended by the National Committee for Clinical Laboratory Standards against penicillin, cefuroxime, ceftriaxone, norfloxacin, t etracycline, kanamycin, spectinomycin, and azithromycin, The MIC of az ithromycin was determined by both the E-test and agar dilution method, All tests were done simultaneously, Results: The MIC of azithromycin to all 135 isolates ranged from 0.078 to 0.25 mu g/ml with the agar di lution method and from 0.016 to 0.50 mu g/ml with the E-test, The MIC5 0 and MIC90 of azithromycin were 0.064 mu g/ml and 0.125 mu g/ml, resp ectively, by the agar dilution method, whereas they are slightly highe r by the E-test method, Seventy-six of the isolates were beta-lactamas e producers and 69 were high-level tetracycline-resistant N,gonorrhoea e, There was no difference in the MIC50 and MIC90 of azithromycin in t hese groups of isolates, The percentage agreement within the acceptabl e +/-1 log(2) dilution difference between MICs obtained by E-test and those obtained by the agar dilution method was 97.8%, Conclusions: Azi thromycin has a very good in vitro antigonococcal activity, and the E- test is a reliable method to determine the MIC of azithromycin against N. gonorrhoeae.