The inhibitory activity of 5-aminolevulinic acid photodynamic therapy (ALA-PDT) on Candida albicans biofilms

Background: Biofilm-associated Candida albicans (C. albicans) infections are hard to cure due to their high levels of resistance to antifungal agents. Photodynamic therapy (PDT) is a promising approach for controlling infections caused by C. albicans. This study was designed to explore the inhibitory activity of PDT using 5-aminolevulinic acid (ALA) as photosensitizer against C. albicans biofilms. Methods: C. albicans cell suspensions were incubated for 48 h to form mature biofilms. ALA solution was diluted to 15 mM and incubated with C. albicans biofilms for 5 h before irradiated by red light semiconductor laser under the light intensity of 300 J/cm2 and fluence rate of 100 mW/cm2 for 50 min. The inhibitory activity was evaluated from subcellular level, molecular level and transcriptional level using transmission electron microscopy (TEM) observation, flow cytometry analysis and quantitative Real-Time Polymerase Chain Reaction (qRTPCR) assays, respectively. Results: From subcellular level, the degraded content of the cytoplasm, nuclear condensation and mitochondrial swelling were observed after ALA-PDT. From molecular level, ALA-PDT resulted in 19.4 % cell apoptosis. From transcriptional level, ALA-PDT significantly reduced the mRNA expressions of hyphae-specific genes (HWP1 and ALS3) and long-term biofilm maintenance genes (UME6 and HGC1), whereas ALA or red light alone had no significant effect. Conclusions: The inhibitory activity indicated that ALA-PDT may have the potential to serve as an antifungal strategy in eliminatingC. albicans biofilms.

Automated summary

The study demonstrated that PDT using 5-aminolevulinic acid as a photosensitizer had significant inhibitory activity against C. albicans biofilms. It induced cell apoptosis, cytoplasm degradation, nuclear condensation, and mitochondrial swelling, and reduced mRNA expressions of specific genes. This suggests that ALA-PDT may serve as a potential antifungal strategy for eliminating C. albicans biofilms.