(described by Salkin, Gordon, Sams, and Rieder in 1982)
Taxonomic Classification
Kingdom: Fungi
Phylum: Ascomycota
Class: Ascomycetes
Order: Saccharomycetales
Family: Saccharomycetaceae
Genus: Blastoschizomyces
Description and Natural Habitats
Blastoschizomyces is a yeast isolated from soil, beach sand, poultry feces, and wood pulp. As well as being an environmental saprobe, it is found in normal microbial flora of human skin, and digestive and respiratory tracts.
Species
The genus Blastoschizomyces currently contains a single species, Blastoschizomyces capitatus.
Synonyms
Blastoschizomyces pseudotrichosporon
Trichosporon capitatum
Geotrichum capitatum
Formerly known as Trichosporon capitatum and classified in Basidiomycetes, this fungus was later found to be more closely related to Ascomycetes based on its cell wall structure, septal pores, G+C content, and production of numerous arthroconidia and few blastoconidia. Its teleomorph Dipodascus capitatus producing ascospores was then discovered, strengthening its classification in class Ascomycetes. Prior to its transfer to the new genus, Blastoschizomyces, this fungus was included in genus Geotrichum. However, its property to produce annelloconidia as well as arthroconidia led to general acceptance of its classification in a new genus, Blastoschizomyces.
Pathogenicity and Clinical Significance
Blastoschizomyces capitatus is an emerging opportunistic fungus potentially pathogenic in cases of immunosuppression [1455]. Neutropenic patients, as well as those receiving chemotherapy, corticosteroids or antibiotics are at risk. Surgery, drug abuse, catheters, and low dose azole treatment have also been reported as predisposing factors [462]. Clinical manifestations of Blastoschizomyces capitatus infections are diverse. Immunocompetent hosts may also develop Blastoschizomyces capitatus infections. Onychomycosis has been reported in an otherwise healthy individual [504]. Infusion of intravenous fluids contaminated with Blastoschizomyces capitatus has been ultimately fatal in a six-month old infant who had no proven immunosuppression [1466].
Fungemia and disseminated infections are likely in immunocompromised hosts [1249, 1251]. The lungs, kidneys, liver, spleen, brain and endocardium may be involved [564, 1247]. Endocarditis, osteomyelitis, meningitis, encephalitis, urinary tract infection, mycetoma and pneumothorax may develop [846, 1247].
Macroscopic Features
Colonies of Blastoschizomyces capitatus grow rapidly and mature in about 5 days. The texture of the colony is yeast-like, and white to cream colored. It becomes mould-like, wrinkled, and develops short aerial hyphae by aging. Blastoschizomyces capitatus can grow at 45°C [462, 1295].
Microscopic Features
On cornmeal tween 80 agar, Blastoschizomyces capitatus produces budding yeast cells, arthroconidia, annelloconidia, true hyphae and pseudohyphae. Oblong annelloconidia, typical for Blastoschizomyces capitatus, are clustered at the tips of the annellides. Annellides are located along or at the tips of the hyphae [462, 1295].
Histopathologic Features
Pleomorphic yeast-like cells (diameter: 3-8 µm) and septate hyphae are visualized in the infected tissue. Arthroconidia may rarely be observed [462].
Compare to
Differentiation of annelloconidia is difficult. They may be misidentified as arthroconidia or blastoconidia. Blastoschizomyces capitatus may mostly be misdiagnosed morphologically as Trichosporon spp., Geotrichum candidum, or Candida krusei. While the lack of urease enzyme activity differentiates it from Trichosporon, its growth at 45°C, resistance to cycloheximide and biochemical characteristics help in definitive identification [462, 1295].
Laboratory Precautions
No special precautions other than general laboratory precautions are required.
Susceptibility
In vitro susceptibility data reported so far are limited. MIC breakpoints for interpretation of in vitro susceptibility results have not been defined. While fluconazole MICs were considerably low [1573], the sordarin compound, GM 237354 [1040], and terbinafine [1990] were also found to be active in vitro against Blastoschizomyces capitatus. Fluconazole and 5-fluorocytosine were more active than amphotericin B and ketoconazole in a comparative in vitro study [2305].
Mortality due to systemic Blastoschizomyces capitatus infections is high. Elimination of the underlying predisposing factors is crucial for clinical cure. None of the available agents are satisfactory for clinical success. Fluconazole therapy may achieve clinical improvement [846].Adjuvant interferon-gamma therapy has been reported to be efficacious in hepatosplenic Blastoschizomyces capitatus infection [564].
For MICs of various antifungal drugs so far reported for Blastoschizomyces capitatus, see our N/A(L):susceptibility database.