Comparative evaluation of etest for susceptibility testing Neisseria meningitidis with eight antimicrobial agents. An investigation using U.S. Food and Drug Administration regulatory criteria.

Invasive infections caused by Neisseria meningitidis continue to be a serious clinical problem for therapy, epidemiology, and potential prophylaxis. Multiple antimicrobial resistances have emerged among meningococcal strains including elevated MICs to penicillin, sulfonamides, tetracyclines, and rifampin. Thus, the need to perform accurate susceptibility testing of meningococci in clinical practice and for surveillance programs has renewed priority. In this study, for the first time Etest (AB Biodisk, Solna, Sweden) was compared to a reference agar dilution method using a large number (100) of clinical strains selected for a range of drug resistances. Etest quantitative accuracy (+/-one log2 dilution agreement) ranged from 94% (penicillin) to 100% (three drugs) for the eight clinically useful antimicrobial agents tested. Intermethod categorical accuracy for all drug ranged from 92% (penicillin, erythromycin) to 100% (five drugs), without false-susceptible or -resistant errors using Etest. Etest and reference methods were highly reproducible (99.6 to 100.0%, respectively). Quantitative discords between methods (> or = two log2 dilutions) were not reproducible and resolved following repeated testing. Etest method proved to be an accurate and reproducible quantitative method for testing N. meningitidis strains for the compared antimicrobial agents (eight) often utilized for therapy and prophylaxis of serious meningococcal disease.