Comparative assessment of Etest for testing susceptibilities of Neisseria gonorrhoeae to penicillin, tetracycline, ceftriaxone, cefotaxime, and ciprofloxacin: Investigation using 510(k) review criteria, recommended by the food and drug administration

We evaluated the ability of the Etest (AB Biodisk, Solna, Sweden) method to accurately and reproducibly determine the antimicrobial susceptibility of Neisseria gonorrhoeae. One hundred gonococcal isolates were used to evaluate the diagnostic performance of the Etest compared with the reference agar dilution method for penicillin tetracycline, ciprofloxacin, cefotaxime, and ceftriaxone. Between 92 and 99% of Etest MIC results for all drugs were within +/-1 log(2) dilution of the reference MIC. According to recommended interpretive criteria, ceftriaxone, cefotaxime, and ciprofloxacin had 100% categorical agreement, while penicillin (86%) and tetracycline (85%) categorical agreement percentages were lower because of the large number of strains that were within 0.5 to 1 log(2) dilution of the susceptible or resistant breakpoints. Reproducibility data also demonstrated that the Etest was precise (99.1%) when subjected to replicate testing. On the basis of these data, the Etest method provides an effective, simple alternative to the reference agar dilution method for the direct quantification of N. gonorrhoeae susceptibility.