Evaluation of the Standardized Disk Diffusion and Agar Dilution Antibiotic Susceptibility Test Methods by Using Strains of Neisseria gonorrhoeae from Tucuman, Argentina

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At present, most Neisseria gonorrhoeae testing is done with β-lactamase and agar dilution tests using common therapeutic agents. Generally, in bacteriological diagnosis laboratories in Argentina, study of antibiotic susceptibility of N. gonorrhoeae is based on β-lactamase determination and agar dilution method using common therapeutic agents. The National Committee for Clinical Laboratory Standards (NCCLS) recently described a disk diffusion test that produces results similar to the reference agar dilution method for antibiotic susceptibility of N. gonorrhoeae. We obtained 57 gonococcal isolates from patients attending a clinic for sexually transmitted diseases in Tucuman, Argentina. Antibiotic susceptibility tests using agar dilution and disk diffusion techniques were compared. The established NCCLS interpretive criteria for both susceptibility methods appeared to be applicable to domestic gonococcal strains. The correlation between the minimum inhibitory concentration (MIC's) and the zones of inhibition was studied for penicillin, ampicillin, cefoxitin, spectinomycin, cefotaxime, cephaloridine, cephalexin, tetracycline, norfloxacin and kanamycin. Dispersion diagrams showed a high correlation between both methods, with a sensitivity of 89% and specificity of 91%.