Comparison of two disc diffusion methods with minimum inhibitory concentration for antimicrobial susceptibility testing of Neisseria gonorrhoeae isolates

Abstract

Background: A few studies are available comparing either minimum inhibitory concentration (MIC) values with the Clinical and Laboratory Standards Institute (CLSI) disc diffusion method or MIC with the Australian Gonococcal Surveillance Program (AGSP) method.
Aim: This study was conducted with the aim to identify the most feasible and cost‑effective method for antimicrobial susceptibility testing of Neisseria gonorrhoeae.
Materials and Methods: Antimicrobial susceptibility testing of N. gonorrhoeae was performed using, in parallel, the E‑test for MIC determination and disc diffusion by CLSI and AGSP techniques, and were compared. Susceptibility to penicillin, ciprofloxacin, tetracycline, ceftriaxone and spectinomycin and cefixime were determined by CSLI and AGSP method and Kappa statistics used to analyse the data with SPSS software.
Results: All isolates were susceptible to ceftriaxone and spectinomycin by three methods. Ninety‑nine (99%) strains were resistant to ciprofloxacin, while 1% showed intermediate susceptibility to ciprofloxacin by all methods. Statistically, there was a moderate level of agreement between the methods for penicillin.
Conclusion: All three methods gave reproducible results. Although the media used in the disc diffusion by the AGSP method is easy and cheap to prepare, the CLSI method of disc diffusion testing is recommended for susceptibility testing of gonococcal isolates because of its feasibility and 100% accuracy, with MIC by E‑test as the reference method.

Keywords: Antimicrobial susceptibility testing, MIC, Neisseria gonorrhoeae