Trichosporon

The taxonomy of Trichosporon has been redefined: Trichosporon cutaneum, T. dermatis, T. jirovecii and T. mucoides have now been transferred to the new genus Cutaneotrichosporon, while Trichosporon domesticum, T. loubieri and T. mycotoxinovorans have now been included into the re-defined genus Apiotrichum (Liu et al. 2015).

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 many have different habitats and usually occupy narrow ecologic niches. Some are soil borne and others are associated with humans and animals (Guarro et al. 1999, Sugita 2011, Arendrup et al. 2015).

Four species Trichosporon asahii, T. asteroides, T. inkin, and T. ovoides are the most common clinical isolates, however, T. cormiiforme, T. dohaense ,T. faecale, T. japonicum and T. lactis have also been reported from human and animal infections (Guarro et al. 1999; Rodriguez-Tudela et al. 2005, Chagas-Neto et al. 2008). Importantly, all species are resistant to echinocandins (Arendrup et al. 2014).

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).

Species descriptions

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