Synergism between the Antidepressant Sertraline and Caspofungin as an Approach to Minimise the Virulence and Resistance in the Dermatophyte Trichophyton rubrum

Abstract

Trichophyton rubrum is responsible for several superficial human mycoses. Novel strategies aimed at controlling this pathogen are being investigated. The objective of this study was to evaluate the antifungal activity of the antidepressant sertraline (SRT), either alone or in combination with caspofungin (CASP). We calculated the minimum inhibitory concentrations of SRT and CASP against T. rubrum. Interactions between SRT and CASP were evaluated using a broth microdilution chequerboard. We assessed the differential expression of T. rubrum cultivated in the presence of SRT or combinations of SRT and CASP. We used MTT and violet crystal assays to compare the effect of SRT alone on T. rubrum biofilms with that of the synergistic combination of SRT and CASP. A human nail infection assay was performed. SRT alone, or in combination with CASP, exhibited antifungal activity against T. rubrum. SRT targets genes involved in the biosyntheses of cell wall and ergosterol. Furthermore, the metabolic activity of the T. rubrum biofilm and its biomass were affected by SRT and the combination of SRT and CASP. SRT alone, or in combination, shows potential as an approach to minimise resistance and reduce virulence.

Keywords: Trichophyton rubrum; antifungal resistance; caspofungin and biofilm; dermatophyte; sertraline; synergistic combinations.

Figure 1

Differentially expressed genes in response to SRT, identified using RT-qPCR analysis. The relative expression of genes TERG_00162 (MFS multidrug transporter), TERG_04234 (Hydrophobin), TERG_06755 (C-8 sterol isomerase), and TERG_12319 (Chitin synthase 2) at 3 h (A) and 12 h (B) are represented. Asterisks indicate the statistical significance of the t-test compared to the control (SB drug absence). * p < 0.05; and ** p < 0.01.

Figure 2

Genes encoding TERG_00162 (MFS multidrug transporter), TERG_04234 (Hydrophobin), TERG_06755 (C-8 sterol isomerase), and TERG_12319 (Chitin synthase 2) are differentially expressed in response to combinations of SRT with CASP. Asterisks indicate statistical significance determined by t-test as compared to the control (SB absence drug) at 3 h (A) and 12 h (B); * p <0.05; ** p < 0.01; *** p < 0.001.

Figure 3

Metabolism of T. rubrum biofilm. Effects of sertraline (SRT), caspofungin (CASP), and SRT + CASP on the metabolic activity of T. rubrum biofilm.

Figure 4

Evaluation of the effect of SRT, CASP, and the synergistic combination (SRT + CASP) on the biomass of T. rubrum biofilm stained with violet crystal. The treatments were performed 3 days after the biofilm matured. Statistical analyses showing significant differences (p < 0.05) between tested compounds and growth control were estimated using one-way ANOVA and Tukey’s post hoc test; ** p < 0.01 and *** p < 0.001.

Figure 5

Effect of SRT, CASP, and SRT + CASP on the biomass of T. rubrum biofilm. Treatments were performed 7 days after the biofilm matured and stained with violet crystal. Significant differences between tested compounds and growth control were obtained using one-way ANOVA and Tukey’s post hoc test. Asterisks indicate statistical significance: ** p < 0.01 and *** p < 0.001.

Figure 6

Scanning electron microscopy of the T. rubrum biofilm on a human nail. T. rubrum strain growth on nail fragments in the absence of drugs (A). Treatment with SRT 50 mg/L (B), SRT 12.5 mg/L (C), CASP 62.50 mg/L (D), CASP 3.90 mg/L (E) and SRT 12.5 mg/L + CASP 3.90 mg/L (F), 20 days of after biofilm matured.