Trichosporon asteroides

Trichosporon asteroides is an asexual Basidiomycetous fungus first described from human skin but is now mainly isolated from blood and urine. "T. asteroides" is a hyphal fungus with a characteristically yeast-like appearance due to the presence of slimy arthroconidia. Infections by this species usually respond to treatment with azoles and amphotericin B.
History and taxonomy.
"Trichosporon asteroides" was isolated from lesion of male chin skin by Rinchin in Berne in 1926 and named in the genus, "Parendomyces". "T. asteroides" was later reevaluated by Masao Ota and transferred to the genus "Trichosporon" as "T. asteroides". Ota noted that its hyphae were more sparsely branched than other species in "Trichosporon", and it lacked the ability to ferment glucose, maltose, sucrose and fructose. Molecular phylogenetic study has since supported the placement of "T. asteroides" in the genus "Trichsporon". "T. asteroides" was determined to be conspecific with "Fissuricella filamenta" on the basis of DNA/DNA reassociation. Modern classifications support the affiliation of this species with the order Tremellales in the phylum Basidiomycota.
Growth and morphology.
"T. asteroides" grows in a range of media including in the presence of the antifungal agent, cycloheximide. Colonies of "T. asteroides" grown on Sabouraud agar appear white in colour with a brain-like texture, reaching a diameter of 10 mm after 10 days growth at . Colonies have radially furrowed outer zone and matt appearance that is not powdery like the related species, "T. asahii". Antibodies produced by infected patients can also be used to differentiate "T. asahii" and "T. asteroides" in disease. Weak growth is seen at but is absent at higher temperatures. "T. asteroides" can be distinguish with other relative species in the genus "Trichosporon" by its ability to utilize D-galactose, L-rhamnose, erythritol and L-arabinitol.
Physiology and pathogenesis.
"T. asteroides" does not ferment glucose, maltose, sucrose or fructose, this is the common feature to all the species in "Trichosporon". "T. asteroides" causes trichosporonosis, which mainly responsible for deep-seated, mucosa-associated, superficial, and systematic infections including blood. This species is one of the three most common "Trichosporon" species isolated in clinical settings. The fungus is sometimes recovered from specimens of blood, urine, and aspiration fluid, vaginal mucosa, male perigenital skin area, and catheters. The first record of this agent in a systemic infection involved a bloodstream infection. Some main types of latent infection can be raised are fungemia, urinary tract infections, peritonitis, endocarditis, arthritis, esophagitis, meningitis, brain abscess, splenic abscess, and uterine infections. Allergies and systemic infections can also be caused by this fungus particularly in immunosuppressed people. Recently, "T. asteroides" was implicated in a case of kerion celsi, a rare, highly inflammatory scalp infection seen mainly in children.
This fungus is rarely encountered in zoonotic infections and has never been shown to cause disease un insects. However, "T. asteroides" was isolated from the multifocal, irregularly raised skin lesions on a female Bottle-Nosed Dolphin, "Tursiops truncatus", in Japan. In the absence of cultures and molecular biological analysis, the agent was initially suspected to be "Paracoccidioides ceti", a worldwide causative agent of Paracoccidioidomycosis in dolphins.
Treatment.
Azole antifungals are often used as a front-line therapy in trichosporonosis. Resistance to amphotericin, flucytosine, fluconazole, and itraconazole have been described. Echinocandins, as a group, are ineffective against "Trichosporon" species. Triazoles show better "in vitro" and "in vivo" antifungal activity than amphotericin B, while voriconazole also has excellent "in vitro" activity against "Trichosporon asteroides". Combination therapy regimens such as voriconazole and amphotericin B are also effective in serious infections. Fluconazole has been used successfully in subcutaneous and deep infections.