Abstract: Objective:?To investigate the effect of methylene-blue-mediated photodynamic therapy (MB-PDT) on the clearance and reformation of biofilms of Enterococcus faecalis (E. faecalis). Methods:?After establishing 24-hour bacterial biofilms of E. faecalis in vitro, the samples were divided into different groups for treatments: 0.9% NaCl; 1% NaClO; MB-PDT; 1% NaClO+MB-PDT; 50 μg/mL MB. Bacteria coating counting method was used to detect the sterility of each group. Scanning electron microscopy and confocal laser microscopy were used to assess the immediate destruction and removal effects of the first four groups on the biofilm. These groups were then allowed to continue treatment to form regenerated biofilms, and MTT and crystal violet staining were employed to detect the metabolic activity and intensity of regenerated biofilm. qRT-PCR was used to analyze the effect of MB-PDT on the expression of genes encoding collagen-binding proteins (ACE), gelatinase (GELE), and serine protease (SPRE) to the mono-species biofilm of E. faecalis. Results: Compared with the control group of 0.9% NaCl, MB-PDT destroyed the biofilm of E. faecalis and significantly reduced the bacteria count (P＜0.05); the strength and activity of the regenerated biofilm were lower than those of the control group (P＜0.05). qRT-PCR showed that the expression of genes related to biofilm formation in E. faecalis was significantly downregulated (P＜0.05). Conclusions: MB-PDT has a destructive effect on biofilms of E. faecalis and inhibits the ability of E. faecalis to reform biofilms.

Key words: Methylene Blue, Photodynamic Therapy, Enterococcus faecalis, Biofilm.