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Published on: February 14, 2018
In vitro susceptibility of Sporothrix schenckii to six antifungal agents determined using three different methods
Eidi Alvarado-Ramírez1, Josep M Torres-Rodríguez
1Infectious Diseases and Mycology Research Unit (URMIM), Institut Municipal d'Investigació Mèdica, Faculty of Medicine, Universitat Autònoma de Barcelona, Barcelona, Spain.
Abstract:
The in vitro susceptibility of Sporothrix schenckii to antifungal drugs has been determined with three different methods. Nineteen Peruvian clinical isolates of S. schenckii were tested against amphotericin B (AB), flucytosine (FC), fluconazole (FZ), itraconazole (IZ), voriconazole (VZ), and ketoconazole (KZ). Modified NCCLS M38-A, Sensititre YeastOne (SYO), and ATB Fungus 2 (ATBF2) methods were used to determine the MICs. ATCC isolates of Candida parapsilosis, Candida krusei, and Aspergillus flavus were used for quality control. Sporothrix inocula were prepared with the mycelial form growing on potato dextrose agar at 28 +/- 2 degrees C. MICs of AB, FC, FZ, and IZ were determined with all three methods, VZ with M38-A and SYO, and KZ with only SYO. The three methods showed high MICs of FZ and FC (MIC(90) of 0.5 microg/ml), being homogeneously lower than those of IZ and KZ. The M38-A method showed a variable MIC range of VZ (4.0 to 16 microg/ml); the geometric mean (GM) was 9.3 mug/ml. The MIC range of AB was wide (0.06 to 16 microg/ml), but the GM was 1.2 microg/ml, suggesting that the MIC is strain dependent. Agreement (two log(2) dilutions) between commercial techniques and the modified M38-A method was very high with FZ, IZ, and FC. In AB and VZ, the agreement was lower, being related to the antifungal concentrations of each method. The highest activity against S. schenckii was found with IZ and KZ. Lack of activity was observed with FZ, VZ, and FC. When AB is indicated for sporotrichosis, the susceptibility of the strain must be analyzed. Commercial quantitative antifungal methods have a limited usefulness in S. schenckii.
Insights
This study evaluated antifungal drug susceptibility for Sporothrix schenckii using three methods. It found itraconazole and ketoconazole most effective, while fluconazole and voriconazole showed limited activity against S. schenckii.
Area of Science:
- Medical Mycology
- Antimicrobial Susceptibility Testing
- Infectious Diseases
Background:
- Sporothrix schenckii is a fungus causing sporotrichosis, a disease requiring effective antifungal treatment.
- Accurate in vitro susceptibility testing is crucial for guiding antifungal therapy selection.
- Evaluating different antifungal agents and testing methodologies is essential for optimizing treatment outcomes.
Purpose of the Study:
- To determine the in vitro antifungal susceptibility of clinical isolates of Sporothrix schenckii.
- To compare the performance of three different antifungal susceptibility testing methods.
- To assess the activity of amphotericin B, flucytosine, fluconazole, itraconazole, voriconazole, and ketoconazole against S. schenckii.
Main Methods:
- Nineteen clinical isolates of Sporothrix schenckii from Peru were tested.
- Antifungal susceptibility was determined using modified NCCLS M38-A, Sensititre YeastOne (SYO), and ATB Fungus 2 (ATBF2) methods.
- Minimum Inhibitory Concentrations (MICs) were determined for various antifungal drugs.
Main Results:
- Itraconazole (IZ) and ketoconazole (KZ) demonstrated the highest in vitro activity against S. schenckii.
- Fluconazole (FZ), voriconazole (VZ), and flucytosine (FC) showed limited activity, with high MICs (MIC(90) of 0.5 µg/ml for FZ and FC).
- Amphotericin B (AB) MICs were strain-dependent, and agreement between commercial methods and the modified M38-A method varied by drug.
Conclusions:
- Itraconazole and ketoconazole are promising agents for treating S. schenckii infections.
- Fluconazole, voriconazole, and flucytosine appear less effective against these clinical isolates.
- When using amphotericin B, antifungal susceptibility testing is recommended due to strain-dependent variability; commercial methods have limited utility for S. schenckii.
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