Photodynamic Inactivation of Streptococcus mutans Using Photosensitizers Based on Curcumin

Objectives: This in vitro study was carried out to evaluate the susceptibility of Streptococcus mutans to phtodynamic inactivation (PDI) using two different photosensitizers based on curcumin and curcuminoids^® solutions by means of minimal inhibitory concentration (MIC) and minimal bactericidal bactericidal concentration (MBC) tests.
Methods: Streptococcus mutans were exposed to LED light at 450nm and 15J/cm² in combination with synthetic curcumin (Bio – Organic Chemistry Laboratory, UFSCAr – Sao Carlos, SP, Brazil) and curcuminoids^® (Sigma Aldrich) solutions at different concentrations (160, 80, 40, 20, 10, 5, 2.5, 1.25, 0.6 and 0.3μM). Radiation-only Groups, photosensitizer alone, and Groups with no treatment were used as controls. Chlorhexidine gluconate at 0.12% (Periogard^®, Colgate) was used as positive control. Before irradiation of the PDI Groups, the photosensitizers remaining in contact with the samples during 5 minutes i. e. pre irradiation time. Serial microdilution method to find minimum inhibitory concentrations (MICs) and with subcultures obtained minimum bactericidal concentrations (MBCs) were performed. Bacterial suspension from each concentration higher than MIC was subcultured onto the surface of BHI (Brain Heart Infusion) agar plates and MBC was assessed. The results were analyzed by analysis of variance and Tukey's test (p<0.05).
Results: PDI with synthetic curcumin and curcuminoids^®, significantly reduced Streptococcus mutans viability under 160-40 and 160-20μM, respectively (p<0.05). In the groups treated just with the photosensitizer or irradiated alone, no significant reduction of Streptococcus mutans colonies was observed. For synthetic curcumin and curcuminoids^® the MIC was 40 and 20μM, respectively (p<0.05). MBC for synthetic curcumin and curcuminoids^® was 80 and 40μM, respectively (p<0.05).
Conclusions: Streptococcus mutans colonies were susceptible to 450nm LED light in the presence of synthetic curcumin and curcuminoids solution.