In vitro study of the antibacterial effects of indocyanine green-mediated photodynamic therapy on Fusobacterium nucleatum biofilms

To investigate the antibacterial effect of a new photosensitizer, indocyanine green (ICG)-mediated photodynamic therapy, on a biofilm of Fusobacterium nucleatum (F. nucleatum) in vitro.

The biocompatibility of the photosensitizer ICG was detected by CCK8. F. nucleatum (10⁸ CFU/mL) was cultured in anaerobic conditions (80% N₂, 10% H₂ and 10% CO₂) mixed with the photosensitizer ICG at concentrations of 0, 10, 20, 30, and 40 μg/mL and then treated with antibacterial photodynamic therapy (808 nm near infrared light with an intensity of 0.1 W/cm² for 3 min), and a mature biofilm was formed after 2 days. The bacteriostatic effects of different concentrations of ICG on F. nucleatum biofilms were compared by colony formation unit count (CFU). The effect of ICG on the formation of F. nucleatum biofilms and biofilm metabolic activity was determined by crystal violet quantification and MTT assays. The effect of ICG on the formation of extracellular polysaccharides in F. nucleatum biofilms was determined by the phenol-sulfuric acid method. The change in the number of bacteria was observed by confocal microscopy.

CFU and biomass of the biofilm gradually decreased with increasing ICG concentration, and there were significant differences compared with the control group. Meanwhile, the metabolic activity of the biofilm and the production of extracellular polysaccharides also showed a significant difference between the ICG groups and the control group (P< 0.01). At the same time, laser confocal microscopy showed that the number of living bacteria decreased gradually.

Antibacterial photodynamic therapy with photosensitizer ICG can effectively inhibit the formation of F. nucleatum biofilms.