Gene Expression of S. mutans Biofilms Submitted to Photodynamic Therapy

Photodynamic Therapy (PDT) presents itself as an alternative option to conventional treatment of dental caries. PDT promotes bacteria death by interaction of a photosensitizer and a light source. Objectives: This study evaluated the antimicrobial potential of PDT and its ability to alter the pattern of gene expression of Streptococcus mutans oral biofilms formed in vitro. Methods: The antimicrobial effect of PDT was obtained using the association of 100ug/mL TBO and the energy density of 55Jcm^-2 of a LED light (620-660nm). S. mutans UA159 biofilms were formed on standard hydroxyapatite discs using the bath culture method with tryptone-yeast extract broth containing 1% of sucrose and incubation at 37°C at 5%CO₂. After 5 days, the biofilms were treated in quadruplicates as follows: without sensitizer and light (S^-L^-); with sensitizer and without light (S⁺L^-); without sensitizer and with light (S^-L⁺) and with sensitizer and light (S⁺L⁺). Biofilms samples were collected; material was disrupted, diluted and plated for counting of oral streptococci. Additionally, remaining biofilms had the total RNA extracted and purified; cDNA synthesized and the real time PCR reaction was performed for genes gtfB, gtfC and gbpB. Results: The microbiological data and gene expression were evaluated by ANOVA and tukey test (α=5%). Microbiologically, a reduction of 5 logs was found in PDT group compared with the controls. PDT did not influence gene expression of gbpB. However, there was a significant reduction in gene expression of gtfC (p<0.01) and gtfB (p<0.05) when biofilms were submitted to PDT. Conclusion: Under tested conditions PDT was effective in killing S. mutans present in biofilms growth in vitro, altering the gene expression patterns of important virulence genes for this microorganism.