Toluidine blue O-mediated antimicrobial photodynamic inactivation reinforced with naringenin against Streptococcus mutans biofilms

BACKGROUND: Combining antimicrobial photodynamic therapy (aPDT) with phytochemicals may enhance antibiofilm activity while reducing reliance on higher photosensitizer concentrations. This study evaluated toluidine blue O (TBO)-mediated aPDT and the adjunctive effect of naringenin (NAR) against Streptococcus mutans biofilms. MATERIALS AND METHODS: ), TBO (100 µg/mL) + LED, TBO (6.25 µg/mL) + LED, NAR + TBO (6.25 µg/mL) + LED, and 0.2 % chlorhexidine (CHX). Colony-forming unit (CFU) and crystal violet staining assays were performed. RESULTS: There was a synergistic interaction at NAR 156.25 µg/mL plus TBO 6.25 µg/mL (FICI = 0.375). Compared with the control, viable counts were significantly lower only in photoactivated TBO (all p < 0.0001). NAR plus TBO (6.25 µg/mL)-aPDT resulted in lower viable counts than TBO (6.25 µg/mL)-aPDT (p < 0.0001) and was not significantly different from TBO (100 µg/mL) + LED (p = 0.69). Crystal violet staining showed reduced biofilm compared to control with TBO (100 µg/mL)-aPDT (p < 0.0001), NAR + TBO (6.25 µg/mL)-aPDT (p < 0.0001), TBO (6.25 µg/mL)-aPDT (p = 0.002), and CHX (p = 0.001). Adding NAR was not significant versus TBO (6.25 µg/mL)-aPDT (p = 0.09) and was comparable to TBO (100 µg/mL)-aPDT (p = 0.51). CONCLUSION: NAR enhanced TBO-aPDT killing of S. mutans biofilms, enabling low-concentration TBO-aPDT to match high-concentration efficacy TBO. Further studies are warranted to confirm efficacy and applicability.