Dematiaceous (Melanized) Molds
1. Describe the dematiaceous fungi, including natural habitat, transmission, and diseases with signs and symptoms.
2. Identify the site where mycetomas are frequently located and the population or populations at risk of infection.
3. Compare and contrast Exophiala jeanselmei and Exophiala dermatitidis, including test methods to distinguish between the two.
4. Describe the microscopic and morphologic features of Pseudallescheria boydii, including its sexual and asexual forms.
5. Differentiate the diagnostic microscopic features of the molds included in this chapter.
Epidemiology and Pathogenesis
Superficial Infections (Tinea Nigra and Black Piedra)
Mycetoma
Two types of mycetomas have been described. Actinomycotic (bacterial) mycetomas are caused by the aerobic actinomycetes, including Nocardia, Actinomadura, and Streptomyces spp. (The aerobic Actinomycetes are described in detail in Chapter 19.) Eumycotic (fungal) mycetomas are caused by a heterogeneous group of fungi that have septate hyphae. Eumycotic mycetomas are subcategorized as white grain mycetomas or black grain mycetomas, a distinction determined by the pigmentation of the infecting agent’s hyphae.
Pathogenesis and Spectrum of Disease
The spectrum of disease caused by the dematiaceous fungi ranges from superficial infections (e.g., skin and hair) to emergent, rapidly progressive, and often fatal disease (e.g., brain abscess). The following list, which is not comprehensive, provides the common etiologic agents of diseases that may be caused by dematiaceous fungi (Table 61-1).
TABLE 61-1
Organism | Disease | Site | Tissue Form |
Slow-Growing Species | |||
Cladosporium spp. | Chromoblastomycosis | Subcutaneous | Sclerotic bodies |
Phaeohyphomycosis | Brain, subcutaneous | Septate hyphae | |
Ochroconis gallopava | Phaeohyphomycosis | Brain, subcutaneous, lungs | Septate hyphae |
Exophiala dermatitidis | Phaeohyphomycosis | Brain, eye, subcutaneous, and dissemination | Hyphal fragments and budding yeast |
Pneumonial | Lungs | ||
Hortaea jeanselmei | Mycetoma phaeomycotic cyst | Subcutaneous | Hyphal fragments and budding yeasts |
Hortaea werneckii | Tinea nigra | Skin | Hyphal fragments and budding yeast |
Fonsecaea spp. | Chromoblastomycosis | Subcutaneous | Sclerotic bodies |
Phaeohyphomycosis | Brain | Septate hyphae | |
Cavitary lung disease | Lungs | Septate hyphae | |
Phialophora spp. | Chromoblastomycosis | Subcutaneous | Sclerotic bodies |
Phaeohyphomycosis | Subcutaneous | Septate hyphae | |
Septic arthritis | Joints | Septate hyphae | |
Piedraia hortae | Black piedra | Hair | Asci-containing nodules cemented to hair shafts |
Madurella mycetomatis | Mycetoma | Subcutaneous | Hyphal fragments |
Rapid-Growing Species | |||
Alternaria spp. | Phaeohyphomycosis | Subcutaneous | Septate hyphae |
Sinusitis | Sinuses | Septate hyphae, possibly fungus ball | |
Nasal septal erosion | Nasal septum | Septate hyphae | |
Ulcers and onychomycosis | Skin, nails | Septate hyphae | |
Bipolaris spp. | Phaeohyphomycosis | Subcutaneous, brain, eye, bones | Septate hyphae |
Sinusitis, fungus ball | Sinuses | Septate hyphae, possibly fungus ball | |
Curvularia spp. | Sinusitis | Sinuses | Septate hyphae; possibly fungus ball |
Phaeohyphomycosis | Subcutaneous, heart valves, eye, and lungs | Septate hyphae | |
Drechslera spp. | Phaeohyphomycosis | Subcutaneous and brain | Septate hyphae |
Sinusitis | Sinuses | Septate hyphae | |
Exserohilum spp. | Phaeohyphomycosis | Subcutaneous | Septate hyphae |
Pseudallescheria boydii | Mycetoma | Subcutaneous | Granules of hyaline hyphae |
Phaeohyphomycosis | Subcutaneous, skin, joints, bones, brain, lungs | Septate, hyaline hyphae | |
Cladophialophora bantiana | Phaeohyphomycosis | Brain | Septate hyphae |
Bacterial: Nocardia, Actinomadura, and Streptomyces spp.
White grain mycetoma: P. boydii and Acremonium and Fusarium spp.
Black grain mycetoma: Madurella mycetomatis, Exophiala jeanselmei, and Curvularia spp.
• Chromoblastomycosis: Cladosporium/Cladophialophora, Phialophora, and Fonsecaea spp.
• Phaeohyphomycosis: E. jeanselmei; Exophiala dermatitidis; and Curvularia, Bipolaris, Alternaria, and Exserohilum spp.
• Sinusitis: Alternaria, Bipolaris, Exserohilum, and Curvularia spp.
• Mycotic keratitis and endophthalmitis: E. dermatitidis and Bipolaris and Curvularia spp.
• Brain abscess: Cladophialophora bantiana, E. dermatitidis, and Bipolaris spp.