Comparative assessment of CDS, CLSI disc diffusion and Etest techniques for antimicrobial susceptibility testing of Neisseria gonorrhoeae: a 6-year study

BACKGROUND: A variety of techniques are available for antimicrobial susceptibility testing of Neisseria gonorrhoeae. OBJECTIVE: The aim of this study was to find a cost-effective, reliable and easily applicable microbiological method to detect antimicrobial susceptibilities of N. gonorrhoeae in resource-poor countries. DESIGN: Prospective study. SETTING: Male and female STD clinic of Regional STD Teaching, Training and Research Centre, New Delhi, India. PARTICIPANTS: N. gonorrhoeae isolates from all male and female patients presenting with acute gonococcal urethritis and cervical discharge. MATERIAL AND METHODS: A total of 295 consecutive N. gonorrhoeae isolates during 2005–2010 was used to compare the Clinical and Laboratory Standards Institute (CLSI) and CDS disc diffusion technique with Etest by performing antimicrobial susceptibility testing in parallel for penicillin, tetracycline, ceftriaxone, ciprofloxacin and spectinomycin. WHO reference strains were used as controls. RESULTS: CDS disc diffusion zones of inhibition showed that complete percentage agreement for penicillin, ciprofloxacin and tetracycline was high with their analogous Etest minimal inhibitory concentrations in comparison to CLSI disc diffusion technique, that is, 91.5%, 92.9% and 99.3% versus 87.5%, 88.5% and 74.9%, respectively. CDS results had less number of major and minor category discrepancies in comparison to CLSI and CDS method showed excellent correlation coefficient (r=1) with Etest for all five antimicrobial agents tested in comparison to CLSI (r=0.92). It was very poor (r=0.61) by CLSI method for tetracycline. The correlation coefficients between the two methods and the Etest were identical if tetracycline was removed from the CLSI analysis. CONCLUSIONS: The CDS technique is an attractive alternative for N. gonorrhoeae susceptibility testing and is recommended for monitoring the antimicrobial susceptibility in less developed and resource-poor settings to facilitate enhanced antimicrobial resistance surveillance when the WHO Gonococcal Antimicrobial Surveillance Programme is undergoing expansion to meet the ongoing challenges of surveillance and control of gonococcal antimicrobial resistance.