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Published on: February 14, 2018
Evaluation of the NCCLS M44-P disk diffusion method for determining susceptibilities of 276 clinical isolates of
M A Pfaller1, S A Messer, L Boyken
1Department of Pathology, Roy J and Lucille A Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA. michael-pfaller@uiowa.edu
Abstract:
We evaluated the NCCLS M44-P fluconazole disk diffusion method in comparison with the NCCLS M27-A2 broth microdilution method for determining the susceptibility of 276 isolates of Cryptococcus neoformans. Disk diffusion testing was performed using Mueller-Hinton agar supplemented with 2% glucose and 0.5 microg of methylene blue/ml. Among the 276 isolates, 259 (93.8%) were susceptible, 16 (5.8%) were susceptible--dose dependent, and 1 (0.4%) was resistant to fluconazole as determined by the NCCLS broth microdilution method. The overall categorical agreement between the two methods was 86%, with 0% very major errors, 2% major errors, and 12% minor errors. The disk diffusion method using Mueller-Hinton agar supplemented with glucose and methylene blue appears to be a useful approach for determining the fluconazole susceptibility of C. neoformans.
Insights
The fluconazole disk diffusion method is a useful approach for determining Cryptococcus neoformans susceptibility. This method showed good agreement with broth microdilution, making it a viable alternative for clinical laboratories.
Area of Science:
- Medical Mycology
- Antimicrobial Susceptibility Testing
Background:
- Cryptococcus neoformans is an opportunistic fungal pathogen.
- Fluconazole is a key antifungal agent for treating cryptococcosis.
- Accurate susceptibility testing is crucial for effective treatment.
Purpose of the Study:
- To evaluate the NCCLS M44-P fluconazole disk diffusion method.
- To compare disk diffusion with the NCCLS M27-A2 broth microdilution method.
- To assess the utility of disk diffusion for C. neoformans susceptibility testing.
Main Methods:
- Disk diffusion testing on Mueller-Hinton agar with glucose and methylene blue.
- Broth microdilution testing according to NCCLS M27-A2 guidelines.
- Analysis of 276 C. neoformans isolates.
Main Results:
- Overall categorical agreement between methods was 86%.
- Disk diffusion showed 0% very major errors and 2% major errors.
- 93.8% of isolates were susceptible to fluconazole by broth microdilution.
Conclusions:
- The disk diffusion method is a potentially useful tool for C. neoformans fluconazole susceptibility.
- The modified disk diffusion method demonstrates good agreement with established methods.
- This offers a practical alternative for clinical settings.
