Photodynamic disruption of a polymicrobial biofilm of two periodontal species using indocyanine green-loaded nanospheres.

Objective: Antimicrobial photodynamic therapy (aPDT) is considered a potential treatment for biofilm infections, which have become an increasing health issue because of the rise in antimicrobial resistance. This study aimed to evaluate the bactericidal effect of aPDT using indocyanine green-loaded nanospheres with chitosan coating (ICG-Nano/c) against polymicrobial periodontal biofilms.

Methods: Composite biofilms of Porphyromonas gingivalis and Streptococcus gordonii were constructed in 96-well plates, and aPDT with ICG-Nano/c and an 810 nm diode laser was performed either by direct irradiation or transmitting irradiation through a 3-mm-thick gingival model. The efficacy of ICG-Nano/c-based aPDT was compared with antibiotics (minocycline and amoxicillin). Additionally, attenuated aPDT under sublethal conditions was used to investigate gene expression related to the antioxidant response (oxyR and sod of P. gingivalis) and biofilm formation via quorum sensing (luxS of both species) with real-time polymerase chain reaction.

Results: ICG-Nano/c-based aPDT significantly reduced the bacterial load in the biofilm, achieving at least a 2 log₁₀ reduction in colony-forming units within 5 minutes for both irradiation methods. After 6 hours of treatment, the bactericidal effects of aPDT and antibiotics were similar, but after 32 hours, antibiotics were more effective, particularly against P. gingivalis. Attenuated aPDT showed a slight increase in sod expression in P. gingivalis, while luxS expression decreased in both bacteria.

Conclusion: The ICG-Nano/c-based aPDT system exerted a certain degree of bactericidal activity against a composite biofilm of periodontal bacteria. Therefore, it has potential as an alternative option or adjunctive therapy to conventional antibiotics in periodontal treatment.