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The medically important dematiaceous fungi and their identification
1Laboratories for Mycology, Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201-0509.
Abstract:
Dematiaceous fungi include a large group of organisms that are darkly pigmented (dark brown, olivaceous, or black). In most cases the pigment is melanin, and specifically, dihydroxynaphthalene melanin. The diseases produced include chromoblastomycosis, eumycotic mycetoma, and phaeohyphomycosis. Phaeohyphomycosis is a new classification for a diverse group of previously known entities grouped together on the basis of finding dematiaceous hyphal and/or yeast-like forms in tissue; tissue involvement may be superficial, cutaneous and corneal, subcutaneous, or systemic. Identification of these fungi is based mostly upon morphology. Important structures include annellides (Phaeoannellomyces, Exophiala), phialides (Phialophora, Wangiella), adelophialides (Phialemonium without collarettes, Lecythophora with collarettes), differentiation of conidiophores (Xylohypha versus Cladosporium) and conidial hilum, septation and germination (Bipolaris, Drechslera, Exserohilum). Useful laboratory tests include the 12% gelatin test (controversial), nitrate assimilation (W. dermatitidis is negative, most other species are positive), and determination of temperature maxima (especially 37 degrees C for E. jeanselmei, 40 degrees C for W. dermatitidis and B. spicifera, 42 degrees C for X. bantiana, and 45 degrees C for Dactylaria constricta var. gallopava and Scedosporium inflatum).
Insights
Dematiaceous fungi, characterized by dark melanin pigment, cause diseases like chromoblastomycosis and phaeohyphomycosis. Identification relies on morphology and laboratory tests, aiding in diagnosing these fungal infections.
Area of Science:
- Medical Mycology
- Infectious Diseases
- Microbiology
Background:
- Dematiaceous fungi are a diverse group of darkly pigmented microorganisms, often containing melanin.
- These fungi are responsible for significant human infections, including chromoblastomycosis, eumycotic mycetoma, and phaeohyphomycosis.
- Phaeohyphomycosis represents a modern classification encompassing various tissue infections caused by dematiaceous fungi.
Purpose of the Study:
- To outline the classification and identification methods for dematiaceous fungi.
- To highlight key morphological features and laboratory tests crucial for diagnosing infections caused by these fungi.
Main Methods:
- Identification primarily relies on morphological examination of fungal structures in tissue, such as annellides, phialides, and conidiophores.
- Distinguishing features include conidial hilum, septation, and germination patterns.
- Laboratory tests such as the 12% gelatin test, nitrate assimilation, and determination of maximal growth temperature are also utilized.
Main Results:
- Morphological analysis reveals distinct structures like annellides, phialides, and adelophialides, aiding in genus differentiation.
- Specific temperature optima and nitrate assimilation patterns provide additional diagnostic clues for species identification.
- The study details key differentiating features for genera like Exophiala, Phialophora, Wangiella, Xylohypha, Cladosporium, Bipolaris, Drechslera, and Exserohilum.
Conclusions:
- Accurate identification of dematiaceous fungi is essential for diagnosing and managing associated diseases.
- A combination of morphological analysis and specialized laboratory tests is critical for effective fungal identification.
- Understanding these diagnostic approaches improves the clinical management of chromoblastomycosis, mycetoma, and phaeohyphomycosis.