Dematiaceous Fungi

The term "dematiaceous" refers to the characteristic dark appearance of this group of fungi as it grows on agar. Colonies are dark gray, brown, or black and, importantly, have a black reverse when the bottom of the agar plate is examined. This distinguishes the dematiaceous fungi from fungi with black conidia but an otherwise pale mycelium, such as A. niger.

Nomenclature and Disease

Phaeohyphomycoses are clinical entities defined by the presence of pigmented hyphae, pseudohyphae, or yeast-like cells in tissue; this is in contrast with the hyalohyphomycoses, which lack pigmentation in tissue sections. Melanin stains can help to identify pigment in poorly-pigmented strains. Chromoblastomycoses, also known as chromomycoses, are chronic infections of the skin and subcutis developing after traumatic implantation of dematiaceous fungi; they are typically fungating, discolored, hemorrhagic lesions. Mycetomas (eumycotic mycetomas) are chronic, localized, progressive infections of the skin, subcutaneous tissue, muscle or bone that are caused by hyaline or dematiaceous fungi; their hallmark is the formation of granules of organized mycelial elements in tissue with the formation of abscesses and draining sinus tracts.
Note that some authors consider chromomycosis and older term for phaeohyphomycosis.

Dematiaceous Fungi: Direct Examination


Dematiaceous fungi can be conveniently divided into three groups based on morphology in slide culture:
  1. macroconidia produced and are divided by longitudinal and transverse septae (these are referred to as muriform macroconidia
  2. macroconidia produced and are divided transverse septae only
  3. microconidia (one celled conidia) produced

Dematiaceous Fungi with Muriform Macroconidia

Alternaria


alternaria

FIG. 1. Note the color of the hyphae and the prominent, multicelled macroconidia. Longitudinal septae are difficult to appreciate at this power.


Ulocladium

ulocladium
ulocladium

FIG. 1. Ulocladium in slide culture. Note muriform septation in the macroconidia indicated by the arrow.

FIG. 1. Ulocladium in slide culture. Again, note the color of the macroconidia and of the hyphae; while hyphae are stained with lactophenol cotton blue stain, macroconidia resist staining in this preparation and appear brown.

ulocladium

Epicoccum


epicoccum

FIG. 1. Epicoccum in slide culture. Sporodochia, conidiophores and small, muriform macroconidia are present.


Dematiaceous Fungi with Transversely Septated Macroconidia


Curvularia


curvularia

FIG. 1. Curvularia in slide culture. Note the characteristic boomerang shaped macroconidia.


Drechslera


drechslera

FIG. 1. Drechslera in slide culture. Macroconidia closely resemble those of Bipolaris


Dematiaceous Fungi with Microconidia

Cladosporium


cladosporium

FIG. 1. Cladosporium in slide culture. Elliptic microconidia are found in long chains.


Phialophora verrucosa

p. verrucosa
phialophora verrucosa

FIG. 1. Phialophora verrucosa in slide culture. Flask-shaped phialides with cup-shaped collarettes and conidia in balls at the apices of the phialides are characteristic.

FIG. 2. Phialophora verrucosa in slide culture. This high power photomicrograph shows a double-flask-shaped phialide; conidia spill from its apex.

phialophora verrucosa

Fonsecaea pedrosoi

f. pedrosoi

FIG. 1. Fonsecaea pedrosoi in slide culture. This figure illustrates so-called fonsecaea-type conidiation: conidiophores are compactly sympodial and bear ovoid primary conidia upon denticles. Primary conidia may support secondary conidia, which in turn may support tertiary conidia, but long chains of conidia-denticle-conidia structures are not seen

fonsecaea pedrosoi

Wangiella dermatitidis

w. dermatitidis
wangiella dermatitidis

FIG. 1. Wangiella dermatitidis in slide culture. Note the absence of collarette on the very slender phialide.


Dematiaceous Fungi that Defy the Above Grouping

Phaeoannellomyces werneckii


phaeoannellomyces werneckii

FIG. 1. Phaeoannellomyces werneckii in slide culture. Note the 2 celled yeast forms.

FIG. 1. Phaeoannellomyces werneckii in slide culture. Note the thick walled hyphae seen in this aging culture.

phaeoannellomyces werneckii

Chaetomium species


FIG. 1. Chaetomium in slide culture. Note the perithecia with radially extending irregular brown filamentous setae

chaetomium

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Copyright © 2001, William McDonald, M.D.
Revised: 3 April 2003