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Disk diffusion susceptibility testing of dermatophytes with imidazoles
1Institute of Microbiology, Madurai Medical College.
Abstract:
In vitro susceptibility testing of 43 isolates of dermatophytes was carried out against imidazoles-ketoconazole, miconazole and econazole and griseofulvin by agar dilution and disk diffusion methods. Econazole was the most effective drug inhibiting all the isolates at a concentration of 0.1 microgram ml-1. The MIC 50s and MIC 90s for ketoconazole and miconazole were 1 and 2.5 mg ml-1 whereas the values for griseofulvin were 1 and 5 micrograms ml-1. Good correlation was seen between the MIC and sizes of zones of inhibition around the disks. Regression analysis was used to measure the degree of correlation between the MIC values and matched averaged zones of inhibition and the correlation coefficients for econazole, ketoconazole, miconazole and griseofulvin were -0.5554, -0.5886, -0.8558 and -0.8268 (p < 0.001) respectively.
Insights
Econazole demonstrated superior in vitro efficacy against dermatophytes, inhibiting all isolates at low concentrations. This study compared antifungal susceptibility testing methods for common treatments.
Area of Science:
- Mycology
- Medical Mycology
- Antimicrobial Susceptibility Testing
Background:
- Dermatophytes are fungi causing superficial infections.
- Antifungal resistance necessitates evaluating drug efficacy.
- Imidazoles and griseofulvin are common antifungal agents.
Purpose of the Study:
- To assess the in vitro susceptibility of dermatophyte isolates to econazole, ketoconazole, miconazole, and griseofulvin.
- To compare the effectiveness of agar dilution and disk diffusion methods for susceptibility testing.
- To evaluate the correlation between minimum inhibitory concentrations (MICs) and zones of inhibition.
Main Methods:
- In vitro susceptibility testing of 43 dermatophyte isolates.
- Agar dilution and disk diffusion methods were employed.
- Antifungal agents tested included econazole, ketoconazole, miconazole, and griseofulvin.
Main Results:
- Econazole was the most potent, inhibiting all isolates at 0.1 µg/mL.
- MIC50 and MIC90 values varied among the tested antifungals.
- A strong negative correlation was observed between MIC values and zones of inhibition for all drugs (p < 0.001).
Conclusions:
- Econazole exhibits significant in vitro activity against dermatophytes.
- Both agar dilution and disk diffusion are reliable methods for susceptibility testing.
- Regression analysis confirms a good correlation between MICs and zone sizes, supporting disk diffusion as a predictive tool.
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