Molecular identification and susceptibility of Trichosporon species isolated from clinical specimens in Qatar: isolation of Trichosporon dohaense Taj-Aldeen, Meis & Boekhout sp. nov

Abstract

Trichosporon species have been reported as emerging pathogens and usually occur in severely immunocompromised patients. In the present work, 27 clinical isolates of Trichosporon species were recovered from 27 patients. The patients were not immunocompromised, except for one with acute myeloid leukemia. Sequence analysis revealed the isolation of Trichosporon dohaense Taj-Aldeen, Meis & Boekhout sp. nov., with CBS 10761(T) as the holotype strain, belonging to the Ovoides clade. In the D1-D2 large-subunit rRNA gene analysis, T. dohaense is a sister species to T. coremiiforme, and in the internal transcribed spacer analysis, the species is basal to the other species of this clade. Molecular identification of the strains yielded 17 T. asahii, 3 T. inkin, 2 T. japonicum, 2 T. faecale, and 3 T. dohaense isolates. The former four species exhibited low MICs for five antifungal azoles but showed high MICs for amphotericin B. T. dohaense demonstrated the lowest amphotericin B MIC (1 mg/liter). For the majority of T. asahii isolates, amphotericin B MICs were high (MIC at which 90% of isolates were inhibited [MIC(90)], > or = 16 mg/liter), and except for fluconazole (MIC(90), 8 mg/liter), the azole MICs were low: MIC(90)s were 0.5 mg/liter for itraconazole, 0.25 mg/liter for voriconazole, 0.25 mg/liter for posaconazole, and 0.125 mg/liter for isavuconazole. The echinocandins, caspofungin and anidulafungin, demonstrated no activity against Trichosporon species.

FIG. 1.

Phylogenetic position of Trichosporon dohaense in the Ovoides clade of the Trichosporonales, based on phylogenetic analysis of the ITS regions of the rRNA gene using PAUP, version 4.0b10, for Macintosh (74). Neighbor-joining analysis was performed with the Kimura 2 substitution model. Strain names and GenBank accession numbers are given after each species name. Next to the tree branches, bootstrap support values after 1,000 replications are given. Clade names are given on the right.

FIG. 2.

Colony morphology of Trichosporon dohaense strain Myco 194 (CBS 10333), grown on SDA+SP at 37°C. (A) Mucoid appearance at an early stage (96 h) of growth; (B) irregular warty growth after 45 days.

FIG. 3.

T. dohaense. (A) Yeast cells (CBS 10671^T). (B) Globose cells with hyphae (CBS 10333) in liquid medium (2% glucose in yeast nitrogen base) after 5 days at 25°C. (C) Arthroconidia and yeast cells (CBS 10333) after 5 days in liquid medium (2% glucose in yeast nitrogen base) at 25°C. (D) Arthroconidia (CBS 10671^T) on cornmeal agar after 10 days at 25°C. Phase-contrast optics were used. Bar, 5 μm.