(described by Leonard & Suggs in 1974)
Taxonomic classification
Kingdom: Fungi
Phylum: Ascomycota
Class: Euascomycetes
Order: Pleosporales
Family: Pleosporaceae
Genus: Exserohilum
Description and Natural Habitats
Exserohilum is a phaeoid or dematiaceous filamentous fungus. It is cosmopolitan in nature inhabiting plant material, particularly grasses, and soil. Teleomorphs are contained within the genus Setosphaeria.
Species
The common clinical species includes E. rostratum and
E. longirostratum.
Exserohilum mcginisii is rarely reported. More than 20 other species are known worldwide, some of which are host-specific.
Synonyms
See the summary of synonyms and teleomorph-anamorph relations for Exserohilum spp.
Pathogenicity and Clinical Significance
Exserohilium is one of many genera that includes causative agents of phaeohyphomycosis. The more common species, E. rostratum, has been reported as an agent of cutaneous disease by Agarwal [17], in a child with leukemia [1559], and mimicking hermorrhagic herpes zoster [2240]. Subcutaneous phaeohyphomycoses were reported by Burges and Hsu [342], [1076]. Two cases of keratitis have been cited [73], [1465], as well as a fatal disseminated infection in a patient with aplastic anemia [110].
E. longirostratum was the etiologic agent in a corneal ulcer [303].
Exserohilum may be pathogenic to some plant species as well as being saprobic to numerous plant hosts, particularly Graminiae (grasses).
Macroscopic Features
Exserohilum species grow rapidly on plant-based medium such as potato dextrose agar and produce woolly colonies that are pale initially but quickly become dark gray, to bluish-black to brownish-black with a black reverse [531], [2202].
Microscopic Features
Hyphae are septate and brown. Conidiophores may be up to 200 µmicro;m long, are septate, simple (non-branched), geniculate, and become paler near the apex. Conidia are various shades of brown and may range from less than 80 to greater than 100 µmicro;m in length, may be straight to distinctly curved, and contain 1 to over 12 septa. The feature all species share is a strongly protruding hilum from the basal cell [2202], [531]. Conidia may be slow to form in culture.
Histopathologic Features
Phaeoid hyphae are frequently moniliform (bead-shaped) in host tissue [415].
Compare to
Bipolaris,
Curvularia,
Dissitimurus,
Helminthosporium,
Drechslera
Key Features for Differentiation
See key features for differentiating
Bipolaris, Curvularia, Drechslera, Exserohilum, and Helminthosporium under the genus description for Bipolaris.
Laboratory Precautions
No special precautions other than general laboratory precautions are required.
Susceptibility
See pages for E. rostratum and E. longirostratum for in vito susceptibility data.