Disk diffusion method for susceptibility testing of Neisseria gonorrhoeae

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Accurate antimicrobial susceptibility testing is vital for guiding Neisseria gonorrhoeae treatment.
• Standardized laboratory methods are essential for reliable Neisseria gonorrhoeae diagnostics.
• Previous studies highlight challenges in Neisseria gonorrhoeae culture and susceptibility testing.

Purpose of the Study:

• To evaluate the standard National Committee for Clinical Laboratory Standards (NCCLS) medium for Neisseria gonorrhoeae disk diffusion and MIC testing.
• To establish zone correlations for current Swedish MIC breakpoints.
• To assess the impact of medium modifications on Neisseria gonorrhoeae growth and test reproducibility.

Main Methods:

• Disk diffusion and Minimum Inhibitory Concentration (MIC) testing of Neisseria gonorrhoeae.
• Evaluation of standard NCCLS medium and a modified medium supplemented with hemoglobin.
• Testing included eight gonococcal control strains and 50 clinical isolates against various antibiotics.

Main Results:

• The standard medium failed to support growth for some Neisseria gonorrhoeae strains, impacting test reliability.
• Supplementing the medium with hemoglobin supported growth for all tested strains.
• Broad MIC ranges were observed for most antibiotics, except ciprofloxacin and spectinomycin, indicating potential interpretive challenges.

Conclusions:

• The standard NCCLS medium requires modification (e.g., addition of hemoglobin) for reliable Neisseria gonorrhoeae susceptibility testing.
• Current MIC breakpoints may need revision due to observed susceptibility distributions and potential for interpretive errors.
• Further clinical evaluation is necessary to refine Neisseria gonorrhoeae treatment guidelines and susceptibility testing parameters.