Dematiaceous

Dematiaceous Fungi

Dematiaceous fungi are a group of fungi characterized by their darkly pigmented hyphae and spores. The pigmentation is due to the presence of melanin in their cell walls, which gives them a dark brown to black appearance. These fungi are commonly found in soil, plant debris, and decaying organic matter. They are of medical importance because some species can cause infections in humans, particularly in immunocompromised individuals.

Characteristics

Dematiaceous fungi are distinguished by their dark pigmentation, which is a result of melanin production. This pigment provides protection against environmental stresses such as ultraviolet radiation and enzymatic degradation. The melanin is deposited in the cell walls, giving the fungi their characteristic dark color.

These fungi can be saprophytic, living on dead organic matter, or pathogenic, causing diseases in plants, animals, and humans. They reproduce both sexually and asexually, with asexual reproduction being more common. The asexual spores, known as conidia, are often pigmented and are produced in various structures such as conidiophores.

Pathogenicity

Dematiaceous fungi are responsible for a range of infections known as phaeohyphomycosis. These infections can be superficial, cutaneous, subcutaneous, or systemic, depending on the species and the host's immune status. Common genera that include pathogenic species are Alternaria, Cladophialophora, Exophiala, and Fonsecaea.

Superficial and Cutaneous Infections

Superficial infections involve the outermost layers of the skin and hair. Tinea nigra, caused by Hortaea werneckii, is a superficial infection characterized by dark brown to black macules on the palms and soles.

Cutaneous infections affect the skin and its appendages. These infections are often chronic and can be difficult to treat.

Subcutaneous Infections

Subcutaneous infections occur when the fungi are introduced into the skin through trauma. Chromoblastomycosis and mycetoma are examples of subcutaneous infections caused by dematiaceous fungi. These infections are characterized by the formation of nodules and plaques, which can ulcerate and become chronic.

Systemic Infections

Systemic infections are rare but can occur in immunocompromised individuals. These infections can affect the lungs, brain, and other organs, leading to severe complications.

Diagnosis

Diagnosis of infections caused by dematiaceous fungi involves clinical examination, histopathological analysis, and culture. The presence of pigmented hyphae in tissue samples is indicative of dematiaceous fungi. Culturing the organism on appropriate media can help identify the specific species.

Treatment

Treatment of infections caused by dematiaceous fungi depends on the type and severity of the infection. Antifungal medications such as itraconazole, voriconazole, and amphotericin B are commonly used. Surgical intervention may be necessary for subcutaneous infections to remove infected tissue.

Also see

• Phaeohyphomycosis
• Chromoblastomycosis
• Mycetoma
• Melanin
• Fungal infections