Precision and accuracy of fluconazole susceptibility testing by broth microdilution, Etest, and disk diffusion...

Area of Science:

• Medical Mycology
• Antimicrobial Susceptibility Testing

Background:

• Accurate antifungal susceptibility testing is crucial for guiding treatment of Candida infections.
• Standard methods like broth microdilution can be time-consuming.
• Evaluating alternative methods for efficiency and accuracy is important.

Purpose of the Study:

• To assess the interpretive agreement of Etest and disk diffusion methods against the fluconazole broth microdilution reference method for Candida species.
• To identify potential challenges and limitations of these methods for specific Candida isolates.

Main Methods:

• Evaluated 495 Candida spp. isolates using fluconazole broth microdilution, Etest, and disk diffusion.
• Assessed agreement between methods and evaluated the impact of incubation time (24h vs. 48h).
• Determined precision by testing 50 isolates in triplicate across three laboratories.

Main Results:

• Etest showed 96% agreement with the reference microdilution method, with mostly minor discrepancies.
• Disk diffusion on Mueller-Hinton agar with additives achieved 97% agreement with the reference method, especially at 24h incubation.
• Certain Candida krusei and Candida glabrata strains required 48h incubation for accurate resistance or growth determination.
• Reproducibility of disk diffusion was comparable to the reference method.

Conclusions:

• Etest and disk diffusion are reliable alternatives to broth microdilution for fluconazole susceptibility testing of Candida.
• Extended incubation times may be necessary for specific Candida species to accurately determine susceptibility.
• Improved methods for endpoint definition are needed to enhance the accuracy of all tested procedures.