Trichosporon dohaense, a rare pathogen of human invasive infections, and literature review

Abstract

Background: Trichosporon dohaense is a rare fungal species that has not been described in human invasive infections.

Patients and methods: In this study, we investigated two T. dohaense isolates from patients with invasive infections in two hospitals in China, as part of the China Hospital Invasive Fungal Surveillance Net (CHIF-NET) program. Both patients were under immunocompromised conditions.

Results: On chromogenic agar, T. dohaense isolates were dark blue, similar to the color of Candida. tropicalis, but the characteristic moist colony appearance was quite different from that of T. asahii. The two isolates were misidentified as T. asahii and T. inkin by the VITEK 2 YST system. The rDNA internal transcribed spacer (ITS) region and the D1/D2 domain sequences of the two T. dohaense isolates were 100% identical to T. dohaense type strain CBS10761^T. The sequence of the intergenic spacer region-1 also clearly distinguished the species. Of the three matrix-assisted laser desorption/ionization time-of-flight mass spectrometry systems, Bruker Biotyper and Autobio MS correctly identified the two isolates to species level, whereas Vitek MS systems misidentified them as T. ovoides or T. asteroides. Echinocandins exhibited no in vitro activities against the two T. dohaense isolates. In addition, the isolates exhibited intermediate susceptibility to fluconazole (with minimal inhibitory concentrations [MICs] of 8 and 16 µg/mL) and itraconazole, voriconazole, and posaconazole (MICs of 0.25-1 µg/mL). T. dohaense demonstrated susceptibility to amphotericin B with MIC of 1 µg/mL. The MICs of fluconazole and voriconazole in our study were higher than the MIC₅₀ of 62 for T. asahii isolates (4 and 0.064 µg/mL) in the CHIF-NET program.

Conclusion: This case study points to a possible emergence of T. dohaense as an opportunistic human invasive fungal pathogen, and the reduced susceptibility should be noted.

Keywords: Trichosporon dohaense; emerging pathogen; identification; invasive infection; reduced susceptibility.

Figure 1

Phenotypic characteristics of two Trichosporon dohaense isolates. Notes: The isolates were grown on Sabouraud dextrose agar (A–D), chromogenic media CHROMagar Candida (E, F) and budding yeast cells, hyphae, and arthroconidia on Sabouraud dextrose agar by periodic acid methenamine silver staining and Gram’s staining, respectively (G, H): Incubation conditions: A, B, and E – 37°C, 48 hours; C, D, and F–H – 37°C, 72 hours; A and C, T. dohaense 10PU193; B and D, T. dohaense 12ZZ130. In E and F, (a) indicates T. dohaense 10PU193; (b) T. dohaense 12ZZ130; (c) T. asahii CBS 2479; (d) C. tropicalis 10H1048; (e) C. albicans ATCC 90028; and (f) C. krusei ATCC 6258. The (d) isolate in panels E and F was selected from the CHIF-NET study. Abbreviation: CHIF-NET, China Hospital Invasive Fungal Surveillance Net.

Figure 2

The MSP dendrogram generated from the protein mass spectra of the two Trichosporon dohaense isolates studied by Bruker Biotyper (Bremen, Germany), version 3.1. Abbreviation: MSP, main spectrum peaks.

Figure 3

The NJ tree of Trichosporon dohaense generated from T. dohaense ITS, D1/D2, and IGS1sequences from this study and the 16 Trichosporon species with clinical relevance available in GenBank, with Cryptococcus neoformans (GenBank accession number EU240005, AF075484, and KC883800, respectively) used as the outgroup. Abbreviations: IGS, intergenic spacer region; ITS, internal transcribed spacer; NJ, neighbor-joining.