Photodynamic Inactivation Effectively Eradicates Biofilm despite Its Interference with the Upregulation of and Efflux Genes.

, in recent years, has emerged as a dangerous nosocomial pathogen. It represents a challenge for effective treatment because of its multiresistance. Photodynamic inactivation (PDI) is a promising way to solve problems with a wide range of resistant microorganisms. This study aimed to use PDI for the eradication of biofilms. Moreover, the regulation of the , , and resistance genes was studied. Experiments were performed on 24 h biofilms formed by three clinical isolates of . PDI was performed in the presence of the photosensitizer methylene blue (0.25 mM) and samples were irradiated with a red laser (λ = 660 nm, 190 mW/cm) for 79, 120, and 300 s. To confirm the PDI effect, confocal laser scanning microscopy was performed after treatment. Effective PDI was achieved in all strains. The highest inhibition was observed after 300 s irradiation, with over 90% inhibition compared with the non-irradiated control sample. PDI was observed to upregulate the expression of the gene, but mainly the gene. Despite this observation, PDI significantly decreased the survival of biofilm cells and proved to have great potential for the eradication of problematic resistant yeasts.