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In vitro susceptibility testing of Fonsecaea pedrosoi to antifungals
C de Bedout1, B L Gómez, A Restrepo
1Sección de Micología, Corporación para Investigaciones Biológicas (CIB), Medellín, Colombia.
Abstract:
Based on the difficulties experienced in the treatment of chromoblastomycosis, 12 primary human isolates of F. pedrosoi, were tested for their in vitro susceptibility to various antimycotics. We adapted the recommendations of the NCCLS for yeasts and followed the indications for mold testing from other authors in order to determine their MIC's and the MLC's. It was found that a significant proportion of the isolates were resistant to 3 of the 4 antimycotics tested, as revealed by high MIC values, as follows: 33% were resistant to amphotericin B (AMB), 58.3% to 5 fluocytosine (5 FC) and 66.7% to fluconazole (FLU). Contrarywise, none of the isolates proved resistant to itraconazole (ITZ). Determination of the MLC's revealed that a larger proportion of the isolates were not killed by AMB, 5 FC (91.7%), FLU (100%) or even, ITZ (41.7%). These data indicate that it would be desirable to determine the susceptibility of F. pedrosoi before initiating therapy, in order to choose the more effective antifungal and avoid clinical failure.
Insights
Most human chromoblastomycosis isolates of Fonsecaea pedrosoi show resistance to common antifungals like amphotericin B, 5-fluorocytosine, and fluconazole. Itraconazole demonstrated effectiveness, suggesting susceptibility testing before treatment is crucial for effective chromoblastomycosis management.
Area of Science:
- Mycology
- Medical Mycology
- Antimicrobial Susceptibility Testing
Background:
- Chromoblastomycosis treatment presents challenges due to antifungal resistance.
- Fonsecaea pedrosoi is a primary causative agent of chromoblastomycosis.
- In vitro antifungal susceptibility data for F. pedrosoi isolates are limited.
Purpose of the Study:
- To evaluate the in vitro susceptibility of primary human isolates of Fonsecaea pedrosoi to four different antimycotic agents.
- To determine the minimum inhibitory concentrations (MICs) and minimum lethal concentrations (MLCs) of tested antifungals against F. pedrosoi.
- To identify the most effective antifungal agent for treating chromoblastomycosis caused by F. pedrosoi.
Main Methods:
- Adapted NCCLS recommendations for yeast testing and mold testing guidelines.
- Determined MICs and MLCs for 12 primary human isolates of F. pedrosoi.
- Tested susceptibility to amphotericin B (AMB), 5-fluorocytosine (5 FC), fluconazole (FLU), and itraconazole (ITZ).
Main Results:
- A significant proportion of F. pedrosoi isolates exhibited resistance to AMB (33%), 5 FC (58.3%), and FLU (66.7%).
- No isolates were resistant to itraconazole (ITZ).
- High percentages of isolates were not killed by AMB, 5 FC, FLU, and ITZ, as indicated by MLC values.
Conclusions:
- Fonsecaea pedrosoi isolates display considerable resistance to commonly used antifungals.
- Itraconazole appears to be the most effective agent against the tested F. pedrosoi isolates.
- Antifungal susceptibility testing prior to therapy is recommended to guide treatment selection and prevent clinical failure in chromoblastomycosis.