Hydrogen peroxide enhances the efficacy of photodynamic therapy against Candida albicans biofilms.

The present study aimed to evaluate the effectiveness of hydrogen peroxide (H2O2) combined with antimicrobial photodynamic therapy (aPDT) on biofilms formed by Candida albicans strains which are either susceptible to or resistant to fluconazole. Biofilms were grown and treated with H2O2, followed by the application of Photodithazine® (P) and red light-emitting diode (LED) (L) either separately or combined (n = 12). After the treatment, biofilms were evaluated by estimating colony-forming unit ml-1, extracellular matrix components [water -soluble and -insoluble polysaccharides, proteins, extracellular DNA (eDNA)], biomass (total and insoluble dry-weight), and protein concentration. Biofilms formed by both strains presented a significant reduction in cell viability, biomass, extracellular matrix components (both types of polysaccharides, eDNA), and proteins (in the soluble and insoluble portion of biofilms) compared to the control. Microscopy images of the biofilms after treatments showed disarticulation of the matrix and scattered fungal cells. The application of H2O2 can disturb the organization of the extracellular matrix, and its association with aPDT potentiated the effect of the treatment.

Antimicrobial photodynamic therapy reduces gene expression of Candida albicans in biofilms.

The present study evaluated whether the oxidative stress caused by antimicrobial photodynamic therapy (aPDT) affects the expression of C. albicans genes related to adhesion and biofilm formation (ALS1 and HPW1) and oxidative stress response (CAP1, CAT1, and SOD1). The aPDT was mediated by two photosensitizing agents (PSs) Photodithazine® (PDZ at 100 and 200 mg/L) or Curcumin (CUR at 40 and 80 µM) and LED (37.5 J/cm2 or 50 J/cm2). The quantification of the expression was performed by Reverse Transcription-Quantitative Polymerase Chain Reaction (RT-qPCR) using specific primers for the target genes. The data were analyzed by Analysis of Variance (α = 0.05), followed by Tukey's post-test. It was observed reduction in the expression of ALS1, HWP1, CAP1, CAT1, and SOD1 when aPDT was performed using 200 mg/L PDZ and 80 µM CUR associated to LED (37.7 and 50 J/cm2, respectively) and using 100 mg/L PDZ and 40 µM CUR with LED of 50 J/cm2 (versus control). Also, the expression of CAP1 and SOD1 genes was reduced after aPDT using 100 mg/L PDZ and LED of 37.5 J/cm2. There was a significant reduction in the expression of genes HWP1, CAP1, and SOD1 after aPDT using 40 µM CUR and 37.5 J/cm2 (versus the control group). The application of LED only at 37.5 and 50 J/cm2 promoted down-regulation of ALS1, CAP1, CAT1, and SOD1 genes (versus the control group). Therefore, aPDT mediated by LED -associated PSs PDZ and CUR promoted a reduction in the expression of the five C. albicans genes evaluated.