Mould Identification: A Virtual Self Assessment

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Colonies (SDA) are white to cream-coloured, powdery, suede-like to farinose with radial furrows and irregular folds.

Hyphae and arthroconidia of Trichosporon asahii.  Budding cells and lateral conidia are absent. Arthroconidia are barrel-shaped. Appressoria absent.

This species assimilates L-arabinose but not melibiose. Growth at 37C.

Comment:
The genus Trichosporon is characterised by the development of hyaline, septate hyphae that fragment into oval or rectangular arthroconidia. Some blastoconidia are also seen. The colonies are usually raised and have a waxy appearance, which develop radial furrows and irregular folds.

Following recent molecular studies, the genus has undergone major revision (Gueho et al. 1992, de Hoog et al. 2000, Rodriguez-Tudela et al. 2005) and 6 species of medical importance are described below. In particular, the name Trichosporon beigelii is now obsolete, and previously described infections reported in the literature under this name could in fact be due to any one of the species listed below.

Trichosporon species are a minor component of normal skin flora, and are widely distributed in nature. They are regularly associated with the soft nodules of white piedra, and have been involved in a variety of opportunistic infections in the immunosuppressed patient. Disseminated infections are most frequently caused by T. asahii and have been associated with leukaemia, organ transplantation, multiple myeloma, aplastic anaemia, lymphoma, solid tumours and AIDS. Disseminated infections are often fulminate and widespread, with lesions occurring in the liver, spleen, lungs and gastrointestinal tract. Infections in non-immunosuppressed patients include endophthalmitis after surgical extraction of cataracts, endocarditis usually following insertion of prosthetic cardiac valves, peritonitis in patients on continuous ambulatory peritoneal dialysis (CAPD), and intravenous drug abuse.

Key to medically important species (de Hoog et al. 2000).

1. Growth with melibiose 2
No growth with melibiose 3

2. Tolerant to cycloheximide T. mucoides
Not tolerant to cycloheximide T. cutaneum

3. Growth with myo-inositol, no growth with L-arabinose T. inkin
No growth with myo-inositol, growth with L-arabinose 4

4. Colony with very slow growth; thallus consisting of clumps of meristematic cells (sarcinae) T. asteroides Colonies and microscopy otherwise 5.

5. Appressoria present in slide cultures T. ovoides Appressoria absent in slide cultures 6.

6. Arthroconidia barrel-shaped; thallus not meristematic T. asahii Arthroconidia elongate, or thallus meristematic T. asteroides.

For further information on Hyalohyphomycosis.

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