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Published on: February 14, 2018
Antifungal Susceptibility Testing and Drug Discovery in the Dimorphic Fungus Histoplasma Capsulatum
1Department of Microbiology, Ohio State University, Columbus, OH, USA. rappleye.1@osu.edu.
Abstract:
The thermal dimorphism of the fungal pathogen Histoplasma is linked to its virulence in mammalian hosts. Mammalian body temperature triggers differentiation of the fungus into virulent yeasts which successfully infect host phagocytes. Accurate determination of antifungal susceptibility with relevance to infection requires that the tests be performed specifically using the yeast form, not the filamentous environmental form. However, traditional CLSI methodology for antifungal susceptibility testing of yeasts with Histoplasma is in adequate. We present optimized methodology for performing antifungal susceptibility assays on Histoplasma yeasts with an emphasis on quantitative yeast growth determination. Colorimetric and fluorometric assays for Histoplasma growth overcome challenges associated with quantifying some Histoplasma strains which grow as aggregates of yeasts. We also describe antifungal susceptibility testing of Histoplasma yeasts within macrophages to provide improved accuracy and better physiological relevance of antifungal susceptibility profiles.
Insights
Accurate antifungal susceptibility testing for Histoplasma yeasts requires optimized methods. New assays improve quantitative growth determination and macrophage-based testing for better infection relevance.
Area of Science:
- Medical Mycology
- Infectious Diseases
- Antifungal Drug Discovery
Background:
- Histoplasma exhibits thermal dimorphism, transitioning from a filamentous form to virulent yeast at mammalian body temperature.
- This yeast form is responsible for histoplasmosis infections in humans, necessitating accurate antifungal susceptibility testing.
- Current standard methods (CLSI) are inadequate for reliable antifungal testing of Histoplasma yeasts.
Purpose of the Study:
- To develop and optimize methodologies for accurate antifungal susceptibility testing of Histoplasma yeasts.
- To address challenges in quantifying yeast growth, particularly for strains forming aggregates.
- To incorporate physiologically relevant models, such as testing within macrophages.
Main Methods:
- Optimization of antifungal susceptibility assays specifically for Histoplasma yeasts.
- Development of colorimetric and fluorometric assays for precise quantitative yeast growth determination.
- Implementation of antifungal susceptibility testing using Histoplasma yeasts internalized within macrophages.
Main Results:
- Established optimized protocols for reliable antifungal susceptibility testing of Histoplasma yeasts.
- Colorimetric and fluorometric assays effectively quantified yeast growth, overcoming aggregation issues.
- Macrophage-based assays provided more accurate and physiologically relevant antifungal susceptibility profiles.
Conclusions:
- Optimized methodologies are crucial for accurate antifungal susceptibility testing of Histoplasma yeasts.
- Novel quantitative growth assays and macrophage models enhance the relevance of antifungal testing for histoplasmosis.
- Improved susceptibility data can guide more effective treatment strategies for Histoplasma infections.
