Susceptibility of Cryptococcus neoformans by the NCCLS microdilution and Etest methods using five defined media

Area of Science:

• Mycology
• Antimicrobial Susceptibility Testing
• Medical Mycology

Background:

• Cryptococcus neoformans is an opportunistic fungal pathogen.
• Antifungal resistance is a growing concern in treating cryptococcosis.
• Standardized susceptibility testing is crucial for guiding therapy.

Purpose of the Study:

• To compare the performance of different culture media and methods for antifungal susceptibility testing of Cryptococcus neoformans.
• To identify optimal conditions for reliable antifungal susceptibility testing of C. neoformans isolates.

Main Methods:

• Testing susceptibility of 12 C. neoformans isolates against five antifungal agents (amphotericin B, 5-fluorocytosine, fluconazole, itraconazole, ketoconazole).
• Utilizing NCCLS and Etest methods.
• Evaluating various media: Yeast Nitrogen Base (YNB) at pH 5.6 and 7.0, RPMI MOPS at pH 7.0 (with and without 2% glucose), and RPMI buffered to pH 7.0.

Main Results:

• Poor growth observed in RPMI MOPS for some isolates after 72 hours.
• Yeast Nitrogen Base (YNB) pH 5.6 proved optimal for 5-fluorocytosine but unsuitable for ketoconazole.
• Both NCCLS and Etest methods showed variability depending on the medium used.

Conclusions:

• Yeast Nitrogen Base (YNB) pH 7.0 or RPMI MOPS with 2% glucose are suitable media for antifungal susceptibility testing of C. neoformans using either NCCLS or Etest methods.
• Careful selection of culture medium is essential for accurate antifungal susceptibility results.
• Further optimization of testing protocols may be needed for specific antifungal agents.