Can sono-photodynamic therapy enhance the antibacterial effect of curcumin against Streptococcus mutans biofilm?

Abstract

Sono-photodynamic therapy (SPDT) is a combined therapy which employs the use of a light source and ultrasound activation for antimicrobial purposes. This study evaluated the antibacterial effect of curcumin-mediated SPDT against Streptococcus mutans biofilm. Absorption spectra of curcumin was determined under UV-visible region (200–800 nm). The generation of reactive oxygen species was evaluated using a fluorescence probe (singlet oxygen sensor green). Minimum inhibitory and minimum bacterial concentrations were determined. S. mutans biofilm was cultured and treated according to the groups as follows: L − PS − U− (negative control), chlorhexidine (positive control), L + PS + U− (aPDT groups), L − PS + U+ (SDT groups), L + PS + U+ (SPDT groups). Before irradiation, the biofilms were incubated for 5 min and irradiated by blue light emitting-diode at 15 J cm−2. For the dark toxicity, the groups were exposed to the same conditions, but no light was used. After treatments, counting of colonies forming units was performed. Confocal microscopy images were obtained. Data were statistically analyzed by ANOVA and Tukey’s test (p ⩽ 0.05). Curcumin under 80 µM showed higher absorption than 40 µM. For the generation of reactive species, antimicrobial photodynamic therapy and SPDT exhibited similar behavior. Minimum inhibitory concentration and minimum bactericidal concentration were 40 and 80 µM, respectively. Curcumin under 40 and 80 µM showed no dark toxicity. SPDT showed better results than isolated therapies, since significant reduction (3.8 log10; p ⩽ 0.001) over the cell viability was observed. This result was confirmed by confocal images. Curcumin showed promising results as a photosensitizer for SPDT. Moreover, curcumin-mediated SPDT exhibited enhanced antibacterial effects and may be an alternative therapy to control the oral biofilm.