Heat-shock proteins (Hsps) are chaperones required for the maintenance of cellular homeostasis in different fungal pathogens, playing an important role in the infectious process. This study investigated the effect of pharmacological inhibition of Hsp90 by radicicol on the Cryptococcus neoformans/Cryptococcus gattii species complex -agents of the most common life-threatening fungal infection amongst immunocompromised patients. The influence of Hsp90 inhibition was investigated regarding in vitro susceptibility to antifungal agents of planktonic and sessile cells, ergosterol concentration, cell membrane integrity, growth at 37 8C, production of virulence factors in vitro, and experimental infection in Caenorhabditis elegans. Hsp90 inhibition inhibited the in vitro growth of planktonic cells of Cryptococcus spp. at concentrations ranging from 0.5 to 2 mg ml 21 and increased the in vitro inhibitory effect of azoles, especially fluconazole (FLC) (P,0.05). Inhibition of Hsp90 also increased the antifungal activity of azoles against biofilm formation and mature biofilms of Cryptococcus spp., notably for Cryptococcus gattii. Furthermore, Hsp90 inhibition compromised the permeability of the cell membrane, and reduced planktonic growth at 37 8C and the capsular size of Cryptococcus spp. In addition, Hsp90 inhibition enhanced the antifungal activity of FLC during experimental infection using Caenorhabditis elegans. Therefore, our results indicate that Hsp90 inhibition can be an important strategy in the development of new antifungal drugs.

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The aim of this study was to determine experimental conditions for in vitro biofilm formation of clinical isolates of Trichosporon inkin, an important opportunistic pathogen in immunocompromised patients. Biofilms were formed in microtitre plates in three different media (RPMI, Sabouraud and CLED), with inocula of 10 4 , 10 5 or 10 6 cells ml 21, at pH 5.5 and 7.0, and at 35 and 28 8C, under static and shaking conditions for 72 h. Growth kinetics of biofilms were evaluated at 6, 24, 48 and 72 h. Biofilm milieu analysis were assessed by counting viable cells and quantification of nucleic acids released into biofilm supernatants. Biofilms were also analysed for proteolytic activity and antifungal resistance against amphotericin B, caspofungin, fluconazole, itraconazole and voriconazole. Finally, ultrastructural characterization of biofilms formed in microtitre plates and catheter disks was performed by scanning electron microscopy. Greater biofilm formation was observed with a starter inoculum of 10 6 cells ml 21, at pH 7.0 at 35 8C and 80 r.p.m., in both RPMI and Sabouraud media. Growth kinetics showed an increase in both viable cells and biomass with increasing incubation time, with maximum production at 48 h. Biofilms were able to disperse viable cells and nucleic acids into the supernatant throughout the developmental cycle. T. inkin biofilms produced more protease than planktonic cells and showed high tolerance to amphotericin B, caspofungin and azole derivatives. Mature biofilms were formed by different morphotypes, such as blastoconidia, arthroconidia and hyphae, in a strain-specific manner. The present article details the multicellular lifestyle of T. inkin and provides perspectives for further research.

This study evaluated the effect of the protease inhibitor ritonavir (RIT) on Trichosporon asahii and Trichosporon inkin. Susceptibility to RIT was assessed by the broth microdilution assay and the effect of RIT on protease activity was evaluated using azoalbumin as substrate. RIT was tested for its anti-biofilm properties and RIT-treated biofilms were assessed regarding protease activity, ultrastructure and matrix composition. In addition, antifungal susceptibility, surface hydrophobicity and biofilm formation were evaluated after pre-incubation of planktonic cells with RIT for 15 days. RIT (200 μg ml) inhibited Trichosporon growth. RIT (100 μg ml) also reduced protease activity of planktonic and biofilm cells, decreased cell adhesion and biofilm formation, and altered the structure of the biofilm and the protein composition of the biofilm matrix. Pre-incubation with RIT (100 μg ml) increased the susceptibility to amphotericin B, and reduced surface hydrophobicity and cell adhesion. These results highlight the importance of proteases as promising therapeutic targets and reinforce the antifungal potential of protease inhibitors.

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These results suggest that antimicrobial therapy may have a direct effect on the pathophysiology of invasive fungal infections in patients at risk.

The aim of this study was to evaluate the effect of promethazine on the antifungal minimum inhibitory concentrations against planktonic cells and mature biofilms of Candida tropicalis, as well as investigate its potential mechanisms of cell damage against this yeast species. Three C. tropicalis isolates (two azole-resistant and one azole-susceptible) were evaluated for their planktonic and biofilm susceptibility to promethazine alone and in combination with itraconazole, fluconazole, voriconazole, amphotericin B, and caspofungin. The antifungal activity of promethazine against C. tropicalis was investigated by performing time-kill curve assays and assessing rhodamine 6G efflux, cell size/granularity, membrane integrity, and mitochondrial transmembrane potential, through flow cytometry. Promethazine showed antifungal activity against planktonic cells and biofilms at concentrations of 64 and 128 μg/ml, respectively. The addition of two subinhibitory concentrations of promethazine reduced the antifungal MICs for all tested azole drugs against planktonic growth, reversing the resistance phenotype to all azoles. Promethazine decreased the efflux of rhodamine 6G in an azole-resistant strain. Moreover, promethazine decreased cell size/granularity and caused membrane damage, and mitochondrial membrane depolarization. In conclusion, promethazine presented synergy with azole antifungals against resistant C. tropicalis and exhibited in vitro cytotoxicity against C. tropicalis, altering cell size/granularity, membrane integrity, and mitochondrial function, demonstrating potential mechanisms of cell damage against this yeast species.

The present study aimed to investigate the inhibitory effect of a bacterial biosurfactant (TIM96) on clinical strains of Trichosporon. Additionally, the effect of TIM96 on the ergosterol content, cell membrane integrity, and the hydrophobicity of planktonic cells was assessed. The inhibitory activity of TIM96 against Trichosporon biofilms was evaluated by analyzing metabolic activity, biomass and morphology. MIC values ranged from 78.125 to 312.5 μg ml for TIM96; time-kill curves revealed that the decline in the number of fungal cells started after incubation for 6 h with TIM96 at both MIC and 2×MIC. The biosurfactant reduced the cellular ergosterol content and altered the membrane permeability and the surface hydrophobicity of planktonic cells. Incubation at 10×MIC TIM96 reduced cell adhesion by up to 96.89%, thus interfering with biofilm formation. This concentration also caused up to a 99.2% reduction in the metabolic activity of mature biofilms. The results indicate potential perspectives for the development of new antifungal strategies.