Variation of Sugar Concentrations Modulates Outcomes of Photodynamic Antimicrobial Chemotherapy

Objective: The present study aimed to assess the effectiveness of Photodynamic Antimicrobial Chemotherapy (PACT) to kill Streptococcus mutans UA 159 biofilm cells grown in the presence of 0.2% or 1% sucrose. Methods: Biofilms were grown on 48 dentin discs for 2 days (18.5 g/L BHI plus 25 mM PIPES, supplemented with 0.2% or 1% sucrose). Biofilm formed at each concentration were divided in 12 groups by combination of following conditions: photosensitizer concentrations (0%, 0.25% or 0.5% Photogem^®, Russia, pH 7.2) and different densities of energy (0, 12, 18 or 24 J/cm²; LED 630 nm, 32 mW/cm², Biotable^®, São Carlos, Brazil). LED equipment allowed irradiating up to 24 samples at the same time and with same parameters. After treatment, aliquots of 50 µL of each sample were inoculated onto BHI agar plates and incubated under anaerobic conditions at 37^oC for 72 h. Results: After 48h, S. mutans counts on dentin discs were similar in biofilms grown in 0.2% (5.68x10⁸) and 1% (2.04x10⁸) sucrose. The combination 0.5% Photogem and 24 J/cm² LED produced the highest reduction of S. mutans counts in both sucrose concentrations. However, results of PACT were better on biofilms grown with 0.2% sucrose (reduced to 7.3x10⁵) than 1% sucrose (reduced to 1.36x10⁷). Besides, a dose-dependent effect of PACT was demonstrated. Conclusion: PACT was more effective in killing S. mutans UA 159 biofilm cells grown in medium supplemented with 0.2% sucrose. This finding suggests that variation of sugar concentrations, hence presumably EPS content, modulates the outcome of Photodynamic Antimicrobial Chemotherapy and that the concentration of carbohydrates during growth of biofilms should be taken into account when results of different in vitro studies on PACT are compared. Sponsorship: FAPESP/Brazil.