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Correlation between E-test, disk diffusion, and microdilution methods for antifungal susceptibility testing of
Madonna J Matar1, Luis Ostrosky-Zeichner, Victor L Paetznick
1Laboratory of Mycology Research, Division of Infectious Diseases, University of Texas-Houston Medical School, Houston, Texas 77030.
Antimicrobial Agents and Chemotherapy
|April 24, 2003
Summary
Agar-based antifungal susceptibility testing methods, including E-test and disk diffusion, reliably identify susceptible Candida isolates to fluconazole. These methods offer a viable alternative to the standard broth microdilution reference for clinical laboratories.
Area of Science:
- Clinical Microbiology
- Mycology
- Infectious Diseases
Background:
- Candida species are common causes of opportunistic fungal infections.
- Accurate antifungal susceptibility testing is crucial for guiding treatment decisions.
- Fluconazole and voriconazole are key antifungal agents used against Candida infections.
Purpose of the Study:
- To evaluate the performance of agar-based methods (E-test, disk diffusion) against the National Committee for Clinical Laboratory Standards (NCCLS) M27-A2 reference method.
- To compare the susceptibility results of fluconazole and voriconazole against Candida isolates using different testing methodologies.
Main Methods:
- Antifungal susceptibility testing of 400 Candida isolates.
- Utilized E-test, disk diffusion, and NCCLS M27-A2 broth microdilution reference methods.
- Compared agreement rates between agar-based and broth microdilution methods for fluconazole and voriconazole.
Main Results:
- Over 96% of fluconazole-susceptible isolates were correctly identified by agar-based methods.
- Lower correlation was observed for resistant isolates identified by agar-based methods.
- Voriconazole showed qualitatively similar results to fluconazole, though interpretive categories are not yet established.
Conclusions:
- E-test and disk diffusion are reliable alternatives to the NCCLS M27-A2 method for identifying fluconazole-susceptible Candida isolates.
- Agar-based methods demonstrate good performance for susceptible categorization, aiding in clinical decision-making.
- Further validation is needed for voriconazole interpretive categories using these methods.