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Trichosporon 

Trichosporon species are urease-positive, non-encapsulated basidiomycetous yeasts 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. They are widely distributed in the environment and many have different habitats, usually occupying narrow ecological niches. Some are soil borne and others are associated with humans and animals (Colombo et al. 2011, Sugita 2011, Arendrup et al. 2014).

The genus has undergone major taxonomic revision (Gueho et al. 1992, de Hoog et al. 2000, Rodriguez-Tudela et al. 2005). 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.

Six species are of clinical significance: T. asahii, T. asteroides, T. cutaneum, T. inkin, T. mucoides and T. ovoides. Other species reported from human and animal infections include T. dermatis, T. domesticum, T. faecale, T. jirovecii, T. loubieri and T. mycotoxinovorans (Rodriguez-Tudela et al. 2005, Chagas-Neto et al. 2008, Colombo et al. 2011).

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 (75%) caused by T. asahii (Arendrup et al. 2014) 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.

Note: 
Genus identification is mandatory for clinical management and should be performed and provided in a timely manner. Species identification remains difficult and requires molecular analysis or MALDI-TOF MS (with an extensive database) (Arendrup et al. 2014).

Molecular Identification: 
ITS and D1/D2 sequencing is required for accurate species identification (Arendrup et al. 2014).

MALDI-TOF MS: 
A promising identification tool to accurately identify species (with an extensive database) (Kolecka et al. 2013).

Comment: 
The API 20C yeast identification system is recommended for sugar assimilation tests.

References: 
Kurtzman and Fell (1988), Gueho et al. (1992), de Hoog et al. (2000, 2015), Rodriguez-Tudela et al. (2005), Chagas-Neto et al. (2008), Guo et al. (2011), Xiao et al. (2013).

Key to medically important species (de Hoog et al. 2000).
1 Growth with melibiose
No growth with melibiose
2
3
2 Tolerant to cycloheximide
Not tolerant to cycloheximide
T. mucoides
T. cutaneum
3

Growth with myo-inositol, no growth with L-arabinose
No growth with myo-inositol, growth with L-arabinose

T. inkin
4
4 Colony very slow growth; thallus consisting of clumps of meristematic cells
Colonies and microscopy otherwise
T. asteroides
5
5 Appressoria present in slide cultures
Appressoria absent in slide cultures
T. ovoides
6
6 Arthroconidia barrel-shaped; thallus not meristematic
Arthroconidia elongate, or thallus meristematic
T. asahii
T. asteroides

Species Descriptions

  • Trichosporon asahii

    RG-2 organism. 

    Morphological Description: 
    Colonies are white to cream-coloured, powdery, suede-like to farinose with radial furrows and irregular folds. Budding cells and lateral conidia are absent. Arthroconidia are barrel-shaped. Appressoria absent. This species assimilates L-arabinose but not melibiose. Growth at 37C. Most common species, especially from invasive infections.

    Physiological Tests: + Positive, - Negative, v Variable, w Weak, s Slow, nd No Data
    Glucose + Melibiose - L-Rhamnose + D-Glucitol v
    Galactose + Raffinose - D-Glucosamine + 𝝰-M-D-glucoside +
    L-Sorbose v Melezitose v NAD-glucosamine + D-Gluconate +
    Sucrose v Soluble Starch v Glycerol v DL-Lactate v
    Maltose + D-Xylose v Erythritol + myo-Inositol v
    Cellobiose + L-Arabinose + Ribitol v Nitrate -
    Trehalose + D-Arabinose + Galactitol - 2-K-D-Gluconate +
    Lactose + D-Ribose + D-Mannitol v D-Glucuronate +

    Antifungal Susceptibility: Trichosporon asahii (Australian National data); MIC µg/mL.
    No <0.03 0.06 0.125 0.25 0.5 1 2 4 8 16 32 >64
    AmB 22 4 4 6 4 3 1
    FLU 22 1 3 11 7
    VORI 20 2 7 10 1
    POSA 19 1 1 11 4 2
    ITRA 22 3 15 3 1
    Note: Non-T. asahii isolates appear to be more susceptible than T. asahii isolates to AmB, FLU, and ITRA, while the new triazoles are active against both T. asahii and non-T. asahii isolates (Rodriguez-Tudela et al. 2005).
  • Trichosporon asteroides

    RG-2 organism. 

    Morphological Description: 
    Colonies are restricted, dry, cream-coloured, cerebriform, with radial furrows and irregular folds. The meristematic form is punctiform, brownish and consists of hyphae which swell and become multiseptate which may fall apart into smaller packets. Budding cells and lateral conidia are absent. Arthroconidia are elongate and hyphae are often present. Appressoria absent. This species assimilates L-arabinose but not myo-inositol. Growth at 37C is variable. Uncommon species usually associated with superficial infections.

    Physiological Tests: + Positive, - Negative, v Variable, w Weak, s Slow, nd No Data
    Glucose + Melibiose - L-Rhamnose + D-Glucitol v
    Galactose + Raffinose - D-Glucosamine v 𝝰-M-D-glucoside +
    L-Sorbose v Melezitose + NAD-glucosamine + D-Gluconate +
    Sucrose + Soluble Starch + Glycerol + DL-Lactate +
    Maltose + D-Xylose + Erythritol + myo-Inositol -
    Cellobiose + L-Arabinose + Ribitol v Nitrate -
    Trehalose + D-Arabinose + Galactitol - 2-K-D-Gluconate +
    Lactose + D-Ribose + D-Mannitol v D-Glucuronate +
  • Trichosporon cutaneum

    RG-2 organism.

    Morphological Description: 
    Colonies are cream-coloured, cerebriform, glabrous, with radial furrows and irregular folds. Budding cells abundant in primary cultures; hyphae developing in older cultures. Arthroconidia are cylindrical to ellipsoidal. Appressoria absent. This species assimilates melibiose; not tolerant to 0.1% (variable tolerance to 0.01%) cycloheximide. No growth at 37C. Uncommon species usually associated with superficial infections.

    Physiological Tests: + Positive, - Negative, v Variable, w Weak, s Slow, nd No Data
    Glucose + Melibiose + L-Rhamnose + D-Glucitol +
    Galactose + Raffinose + D-Glucosamine v 𝝰-M-D-glucoside +
    L-Sorbose v Melezitose + NAD-glucosamine + D-Gluconate +
    Sucrose + Soluble Starch + Glycerol + DL-Lactate +
    Maltose + D-Xylose + Erythritol + myo-Inositol +
    Cellobiose + L-Arabinose + Ribitol + Nitrate -
    Trehalose + D-Arabinose v Galactitol - 2-K-D-Gluconate +
    Lactose + D-Ribose + D-Mannitol + D-Glucuronate +
  • Trichosporon inkin

    RG-2 organism.

    Morphological Description: 
    Colonies are restricted, white, finely cerebriform with a granular covering, without marginal zone, often cracking the media. Budding cells and lateral conidia absent. Arthroconidia are long cylindrical. Appressoria present in slide cultures. Sarcinae present on media with high sugar-content. This species assimilates myo-inositol but not melibiose and is tolerant to 0.01% (variable tolerance to 0.1%) cycloheximide. Growth at 37C. Usually associated with white piedra on pubic hairs.

    Physiological Tests: + Positive, - Negative, v Variable, w Weak, s Slow, nd No Data
    Glucose + Melibiose + L-Rhamnose - D-Glucitol +
    Galactose v Raffinose + D-Glucosamine v 𝝰-M-D-glucoside +
    L-Sorbose v Melezitose + NAD-glucosamine + D-Gluconate +
    Sucrose + Soluble Starch + Glycerol v DL-Lactate +
    Maltose + D-Xylose + Erythritol + myo-Inositol +
    Cellobiose + L-Arabinose + Ribitol - Nitrate -
    Trehalose + D-Arabinose + Galactitol - 2-K-D-Gluconate +
    Lactose + D-Ribose + D-Mannitol v D-Glucuronate +
  • Trichosporon mucoides

    RG-2 organism. 

    Morphological Description: 
    Colonies are moist and glabrous, white, cerebriform, heaped and folded. Budding cells present in primary cultures. Broadly clavate, terminal or lateral blastoconidia often present, becoming thick-walled with age. Arthroconidia are barrel-shaped. Appressoria absent. This species assimilates melibiose and is tolerant to 0.01% (variable tolerance to 0.1%) cycloheximide. Growth at 37C. Common species associated with superficial infections, white piedra and onychomycosis.

    Physiological Tests: + Positive, - Negative, v Variable, w Weak, s Slow, nd No Data
    Glucose + Melibiose + L-Rhamnose + D-Glucitol +
    Galactose + Raffinose + D-Glucosamine + 𝝰-M-D-glucoside +
    L-Sorbose + Melezitose + NAD-glucosamine + D-Gluconate +
    Sucrose + Soluble Starch + Glycerol + DL-Lactate +
    Maltose + D-Xylose + Erythritol + myo-Inositol +
    Cellobiose + L-Arabinose + Ribitol + Nitrate -
    Trehalose + D-Arabinose + Galactitol + 2-K-D-Gluconate +
    Lactose + D-Ribose + D-Mannitol + D-Glucuronate +
  • Trichosporon ovoides

    RG-2 organism. 

    Morphological Description: 
    Colonies are restricted, white, granular, folded at the centre, with a flat marginal zone. Budding cells and lateral conidia absent. Arthroconidia are cylindrical. Appressoria present in slide cultures. This species does not assimilate melibiose, but tolerates 0.01% cycloheximide. Growth at 37C is variable. Uncommon species usually associated with superficial infections, like white piedra.

    Physiological Tests: + Positive, - Negative, v Variable, w Weak, s Slow, nd No Data
    Glucose + Melibiose - L-Rhamnose + D-Glucitol v
    Galactose + Raffinose v D-Glucosamine v 𝝰-M-D-glucoside +
    L-Sorbose v Melezitose v NAD-glucosamine + D-Gluconate +
    Sucrose + Soluble Starch + Glycerol v DL-Lactate +
    Maltose + D-Xylose + Erythritol + myo-Inositol +
    Cellobiose + L-Arabinose v Ribitol - Nitrate -
    Trehalose v D-Arabinose v Galactitol - 2-K-D-Gluconate +
    Lactose + D-Ribose + D-Mannitol + D-Glucuronate +

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