Apiotrichum

In a taxonomic revision of Trichosporon, Liu et al. (2015) re-defined the genus Apiotrichum to include the pathogenic species Apiotricum domesticum, A. loubieri and A. mycotoxinovirans.

Apiotrichum are urease-positive, non-encapsulated basidiomycetous yeasts characterised by the development of hyaline, septate hyphae that fragment into oval or rectangular arthroconidia. This makes morphological identification difficult and molecular identification is often required. Importantly, all species are resistant to echinocandins and other classes of antifungal agents (Arendrup et al. 2014).

Apiotrichum species are often isolated from human and animal sources as well as clinical specimens, some of them being associated with opportunistic infections. It is also worth mentioning that the pathogenic species all have the ability to grow at 37 °C. Fermentation is absent. 

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. 2015).

Molecular identification:  Species identification requires sequence analysis of the D1/D2 domains and the ITS 1 + 2 regions of the rDNA.  (Sugita et al. 1999, Arendrup et al. 2015).

MALDI-TOF-MS:  appears to be a promising identification tool (with an extensive database) (Kolecka et al.2013).

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

Species descriptions

  • Apiotrichum domesticum

    Synonym: Trichosporon domesticum

    Apiotrichum domesticum may occur widely in the environment, including the extreme habitat of soils in the Antarctica Dry Valleys (Fell et al. 2006). The species is frequently isolated from the houses of patients suffering from summer-type hypersensitivity pneumonitis (Sugita et al. 2004). A. domesticum has been isolated from the urine of a cat with chronic cystitis (Sakamoto et al. 2001), but the pathogenicity of this species remains unknown.

    Morphological description: 
    Colonies (SDA) are cream to pale yellow, semi-shiny, pustular to cerebriform, and with the margin fringed with hyphae. Yeast cells are globose or ovoid and occur singly or in pairs. Septate hyphae with arthroconidia are present. D-gluconate not assimilated but tolerates 0.1% cycloheximide. Growth at 37OC. 

    RG-2 organism.

    Physiological Tests: + Positive, - Negative, v Variable, w Weak, s Slow, nd No Data
    Glucose + Melibiose - L-Rhamnose - D-Glucitol v
    Galactose + Raffinose - D-Glucosamime + 𝝰-M-D-Glucoside +
    L-Sorbose v Melezitose + N-A-D-glucosamine nd 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 s D-Glucuronate -
  • Apiotrichum loubieri

    Synonym: Trichosporon loubieri

    Apiotrichum loubieri was originally described by Morenz (1963) from a strain isolated from cow mastitis and has also been reported from the extreme environment of soils in the Antarctic Dry Valleys (Fell et al. 2006). Although the pathogenicity of this species is not known, two cases of infection caused by A. loubieri have been reported (Marty et al. 2003, Padhye et al. 2003).

    Morphological description:
    Colonies (SDA) are whitish, semi-shiny to dull-shiny, and have a fringed margin. Yeast cells are globose or ovoid, and occur singly or in pairs. Septate hyphae with arthroconidia are present. Arthroconidia are cubic and short-cylindrical. Tolerates 0.1% cycloheximide and growth at 42C. 

    Apiotrichum loubieri and Trichophosporon inkin are both able to grow at 42C. However, A. loubieri can be distinguished from the latter by its ability to use salicin, melibiose or D-glucono-1,5-lactone, which cannot be assimilated by T. inkin.

    RG-2 organism.

    Physiological Tests: + Positive, - Negative, v Variable, w Weak, s Slow, nd No Data
    Glucose + Melibiose + L-Rhamnose + D-Glucitol +
    Galactose + Raffinose + D-Glucosamime + 𝝰-M-D-Glucoside +
    L-Sorbose - Melezitose - N-A-D-glucosamine nd 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 + D-Glucuronate +
  • Apiotrichum mycotoxinivorans

    Synonym: Trichosporon mycotoxinivorans

    Apiotrichum (Trichosporon) mycotoxinivorans was described by Molnár et al. (2004) from a strain isolated from cultivated termites. The species can be distinguished from other species by the ability to assimilate a combination of sucrose, melibiose, galactitol and propane 1,2 diol. In addition, it can detoxify mycotoxins such as ochratoxin A and zearalenone (Molnár et al. 2004).

    RG-2 organism.

    Morphological description:
    Culture (SDA) is whitish, dull, smooth, flat and velutinous, with a margin fringed with hyphae. Yeast cells are globose or ovoid and occur singly or in pairs. Septate hyphae with arthroconidia are present. Arthroconidia are cubic and cylindrical.  Tolerates 0.1% cycloheximide and growth at 37C. 

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