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Mould Identification: A Virtual Self Assessment

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Unknown 18 = Exophiala dermatitidis

Case History
A 60 year-old male presented with a subcutaneous lesion on the sole of his right foot. A single draining sinus was present which yielded several black grains.Cultures grew the fungus shown below.
Culture (note good growth at 40C)

Colonies are slow growing, initially black and yeast-like, becoming suede-like, olivaceous grey and mould-like with age. Cultures grow at 42C.
Microscopy

An initial yeast-like phase is characterized by unicellular, ovoid to elliptical, budding yeast-like cells. With the development of mycelium, flask-shaped to cylindrical annellides are produced. Spherical phialiees with large, fragile collaretts may also be present (not seen in this strain). Conidia are hyaline to pale brown, one-celled, round to obovoid, 2.0-4.0 x 2.5-6.0 um, smooth-walled and accumulate in slimy balls (glioconidia) at the apices of the phialides or down their sides.

The identity of this isolate was confirmed by sequencing the the D1/D2 region of large subunit rRNA. The strain showed >99.8% identity to numerous E. dermatitidis strains including strains from CBS while it only shows 97.5% ID to Exophiala jeanselmei.

Comment: Exophiala dermatitidis has been isolated from plant debris and soil and is a recognized causative agent of mycetoma and phaeohyphomycosis in humans. Clinical manifestations include subcutaneous cystic lesions, endocarditis and brain abscesses. E. dermatitidis is neurotropic and cerebral infections are frequently seen.

About Exophiala Back to Virtual Assessment

What is your identification?

Phialophora repens
Phaeoacremonium paratiticum
Exophiala dermatitidis

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Dr David Ellis
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