Objective:To evaluate the effect of microevolution on phenotypes and drug resistance of the Trichosporon asahii biofilm. Methods:The standard strain of Trichosporon asahii was obtained from the Fungal Biodiversity Institute of the Royal Netherlands Academy of Arts and Sciences, the fluconazole-sensitive primary strain (TO) of Trichosporon asahii was isolated from a case of trichosporonosis diagnosed in the Department of Dermatology, the Seventh Medical Center of Chinese People′s Liberation Army General Hospital in 2000, and the fluconazole-resistant evolved strain (TEVO) of Trichosporon asahii was isolated from the above patient in 2014. Biofilms of the above-mentioned strains were formed in vitro, and tetrazolium salt XTT reduction assay was performed to evaluate growth kinetics of the Trichosporon asahii biofilm, and laser scanning confocal microscopy to determine the thickness of the biofilm; the sessile minimum inhibitory concentrations (SMICs) of fluconazole, itraconazole and voriconazole against the biofilms at different growth stages were determined in vitro for the evaluation of the resistance of the biofilms. One-way analysis of variance was used for comparisons among multiple groups, and Hartley test for testing homogeneity of variance. If the variance was homogeneous, least significant difference test was used for multiple comparisons; if the variance was heterogeneous, Tamhane′ T2 test was used for multiple comparisons. Results:In the adhesion (0 h) and formation stages (4- 24 hours) of the Trichosporon asahii biofilm, the metabolic activity of the evolved strain TEVO was the weakest (adhesion stage: F = 35.705, P < 0.001; formation stage: F = 15.042, P < 0.001) . At 48 hours after adhesion, the biofilms matured, and the TO strain showed the weakest metabolic activity ( F = 10.985, P < 0.001) . In the maturation stage, the biofilm thickness of the TEVO strain (26.1 ± 1.18 μm) was significantly higher than that of the TO strain (22.8 ± 1.73 μm, P = 0.001) , but significantly lower than that of the standard strain (29.5 ± 1.28 μm, P = 0.001) . As drug susceptibility testing showed, the SMICs of azole antifungal agents against the TEVO strain were higher than those against the TO strain in the adhesion and formation stages of the Trichosporon asahii biofilm, and the SMICs of azole antifungal agents against the biofilms of the 3 strains of Trichosporon asahii were all over 1 024 mg/L in the maturation stage of the biofilm. Conclusion:Under the dual pressure of host environment and antifungal drugs, adaptive changes took place in the phenotypes of the Trichosporon asahii biofilm with an increase in the resistance to azole antifungal drugs.

The opportunistic fungal pathogen Trichosporon asahii (T. asahii) is an important causal agent of mortality in immunocompromised patients and associated with frequent relapses, even with sufficient antifungal treatment. Investigating the proteomes of initial and recurrent isolates may help to identify within-host adaptive changes. In this study, using tandem mass tag (TMT)-labeling combined with liquid chromatography-mass spectrometry/ mass spectrometry (LC-MS/MS) technology, we analyzed the proteomes of two T. asahii strains that were isolated 15 years apart from the same patient who suffered initial and recurrent episodes of systemic disseminated trichosporonosis. A total of 597 differentially expressed proteins were identified. Functional analysis showed that the increased proteins were primarily concentrated on peptide/protein/energy/drug metabolism and translation. Most of the results were determined to be consistent with the findings of phenotypic assays, such as tests for drug susceptibility, temperature growth, biofilm formation, melanization and paromomycin assays. Moreover, we performed multiple reaction monitoring (MRM) mass spectrometry to verify 27 candidate proteins, and the results of this experiment were also highly consistent with the results of the TMT analysis. Therefore, to the best of our knowledge, these data provide the first molecular evidence of how the T. asahii proteome changes related to host-specific adaptation during human infection. Significance: Systemic infection with Trichosporon asahii (T. asahii) has recently been recognized as an important causal agent of mortality in immunocompromised patients. Although triazole treatment usually works efficiently in the early phase of infection, many patients relapse. Hence, comparative analyses of the proteomics of initial and recurrent isolates may reveal evidence of adaptive changes within the host. Our study demonstrates that the recurrent strain has undergone proteomic changes using tandem mass tag (TMT)-labeling combined with liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Moreover, the results of phenotypic assays, including drug susceptibility, temperature growth, biofilm formation, melanization and paromomycin assays, were highly consistent with the proteomic changes, and multiple reaction monitoring (MRM) verification also showed similar trends to the TMT results. In summary, our study is the first to investigate the adaptation of T. asahii under pressure from antifungal chemotherapy and host immune responses.

Trichosporon asahii infection is difficult to control clinically. This study identified a case with over 15 years of T. asahii infection-related systemic dissemination disease and conducted genome and transcriptome sequencing to identify fluconazole-resistant genes in fluconazole-resistant versus susceptible strains isolated from this patient's facial skin lesions. The data revealed mutations of the ergosterol biosynthetic pathway-related genes in the T. asahii genome of the fluconazole-resistant strain, that is, there were 36 novel mutations of the ERG11 gene, three point mutations (V458L, D457V, and D334S) in the ERG3, and a missense mutation (E349D) in ERG5 in the fluconazole-resistant strain of the T. asahii genome. To ensure that ERG11 is responsible for the fluconazole resistance, we thus simultaneously cultured the strains in vitro and cloned the ERG11 CDS sequences of both fluconazole-susceptible and -resistant strains into the Saccharomyces cerevisiae. These experiments confirmed that these mutations of ERG11 gene affected fluconazole resistance (> 64 μg/ml vs. <8 μg/ml of the MIC value between fluconazole-resistant and -susceptible strains) in Saccharomyces cerevisiae. In addition, expression of ergosterol biosynthesis pathway genes and drug transporter was upregulated in the fluconazole-resistant strain of T. asahii. Collectively, the fluconazole resistance in this female patient was associated with mutations of ERG11, ERG3, and ERG5 and the differential expression of drug transporter and fatty acid metabolic genes.

Objective To investigate the role of the ERG11 gene in the drug resistance of Trichosporon asahii (T.asahii), and to explore the relationship between the gene expression and drug concentrations. Methods Stable fluconazole-resistant strains of T.asahii were induced in vitro following exposure to a series of concentrations of fluconazole. Fluconazole-sensitive and-resistant strains of T.asahii were separately cultured in the medium containing fluconazole at concentrations of 0, 0.25, 0.5, 1, 2, 4, 8, 16, 32 and 64 μg/ml. Real-time quantitative PCR was performed to determine the mRNA expression of ERG11 gene. Results In fluconazole-free medium, the fluconazole-resistant strain of T.asahii showed significantly increased mRNA expression of the ERG11 gene compared with the fluconazole-sensitive strain (7.542 ± 5.311 vs. 1.014 ± 0.012, t=3.002, P=0.03). Additionally, the mRNA expression of ERG11 gene was also significantly higher in the fluconazole-resistant strains than the fluconazole-sensitive strains in the culture medium containing fluconazole at different concentrations of 0.25 (9.183 ± 3.226 vs. 3.281 ± 2.068), 0.5(13.657 ± 5.428 vs. 3.459 ± 1.923), 1(15.292 ± 7.007 vs. 3.242 ± 2.530), 2(13.720 ± 8.550 vs. 3.651 ± 0.728), 4(13.949 ± 2.960 vs. 3.969 ± 1.924)and 8(13.123 ± 6.429 vs. 3.824 ± 1.875)μg/ml(all P<0.05). However, no significant correlation was observed between the mRNA expression of ERG11 gene and fluconazole concentrations(fluconazole-resistant strains: rs = 0.229, P = 0.096; fluconazole-sensitive strains:rs=0.166, P=0.357). Conclusion Overexpression of ERG11 gene is associated with fluconazole resistance in T.asahii, but there is no correlation between the mRNA expression of ERG11 gene and fluconazole concentrations.

Background/Purpose: Silver nanoparticles are receiving increasing attention in biomedical applications. This study aims at evaluating the antifungal properties of silver nanoparticles against the pathogenic fungus Trichosporon asahii.Methods: The growth of T. asahii on potato dextrose agar medium containing different concentrations of silver nanoparticles was examined and the antifungal effect was evaluated using minimum inhibitory concentration. Scanning and transmission electron microscopy were also used to investigate the antifungal effect of silver nanoparticles on T. asahii.Results: Silver nanoparticles had a significant inhibitory effect on the growth of T. asahii. The minimum inhibitory concentration of silver nanoparticles against T. asahii was 0.5 ug/mL, which was lower than amphotericin B, 5-flucytosine, caspofungin, terbinafine, fluconazole, and itraconazole and higher than voriconazole. Silver nanoparticles obviously damaged the cell wall, cell membrane, mitochondria, chromatin, and ribosome.Conclusion: Our results demonstrate that silver nanoparticles have good antifungal activity against T. asahii. Based on our electron microscopy observations, silver nanoparticles may inhibit the growth of T. asahii by permeating the fungal cell and damaging the cell wall and cellular components. Copyright (C) 2014, Taiwan Society of Microbiology. Published by Elsevier Taiwan LLC. All rights reserved.