Exophiala jeanselmei
| Exophiala jeanselmei | |
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| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Eurotiomycetes |
| Order: | Chaetothyriales |
| Family: | Herpotrichiellaceae |
| Genus: | Exophiala |
| Species: | E. jeanselmei |
| Binomial name | |
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Exophiala jeanselmei (Langeron) McGinnis & A.A.Padhye (1977) |
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| Synonyms | |
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Exophiala jeanselmei is a saprotrophic fungus in the family Herpotrichiellaceae. Four varieties have been discovered: Exophiala jeanselmei var. heteromorpha, E. jeanselmei var. lecanii-corni, E. jeanselmei var. jeanselmei, and E. jeanselmei var. castellanii. Other species in the genus Exophiala such as E. dermatitidis and E. spinifera have been reported to have similar annellidic conidiogenesis and may therefore be difficult to differentiate.
Exophiala jeanselmei was first isolated in 1928 by Jeanselme from a case of black mycetoma on the foot. The nomenclature was based on the fungus' morphological characteristics, hence, it was originally classified as Torula jeanselmei because of its yeast like shape when grown in culture. It was later reclassified by McGinnis and Padhye in 1977 as Exophiala jeanselmei after further research on conidiogenesis.
In culture, E. jeanselmei produces slow growing colonies that are green black in color. Cultures manifest a combination of mycelial and yeast-like growth forms, however the yeast-like typically predominates. Black aerial mycelium develops on the colony surface that consists of hyphae with swellings at regular intervals. Conidia are variable in size and are often formed in clusters at the tip of annellidic conidiogenous cells. The conidia are narrowly ellipsoidal in shape and 2.6-5.9 µm × 1.2-2.5 µm in size. Immature sexual fruiting bodies called ascomata have been reported but their rare occurrence are thought to be due to the lack of mating compatibility.Exophiala jeanselmei is affiliated with the ascomycete genus Capronia.
Exophiala jeanselmei is commonly found in soil, plants, water, and can also be isolated from decaying wood as this fungus is a saprotroph in nature. This species has world-wide occurrence but are particularly noted in Asia and more commonly in tropical and subtropical regions. The genus Exophiala has been isolated from hydrocarbon rich environments as well as from hot, humid, and oligotrophic environments such as dishwashers, steam bath facilities and bathrooms that only provide low levels of nutrients. It has been proposed that the conditions usually found within dishwashers such as high temperature, moisture and alkaline pH can provide an alternative habitat for human pathogenic species. The fungus has optimal growth at 30 °C but growth is inhibited at 40 °C. Most strains isolated from soil cannot grow at temperatures higher than 30 °C while strains isolated from humans can grow at higher temperatures such as 37 °C of the human body. This adaptation of E. jeanselmei had developed evolutionarily in order to survive on their human hosts. This is a distinguishing factor that helps in determining the pathogenicity of a particular strain. A feature that distinguishes E. jeanselmei from Cladosporium which forms very similar colonies is that E. jeanselmei is not proteolytic. It is able to assimilate glucose, galactose, maltose, and sucrose, but not lactose.
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