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OBJECTIVE The objective of this study was to inhibit thePseudomonas aeruginosa biofilm through curcumin-mediated antimicrobial photodynamic therapy (APDT). BACKGROUND The mechanism behind APDT mediated photoinactivation depend upon reactive oxygen species (ROS) production, like singlet oxygen and free radicles. METHODS To evaluate the antibacterial efficacy of curcumin induced APDT onP. aeruginosa by colony forming unit (CFU) while antibiofilm action was determined by the use of crystal violet, XTT, congored binding assay and confocal laser scanning microscope (CLSM). RESULTS We found that curcumin with 10 J/cm2 of light reduces P. aeruginosa biofilm more efficiently than without light. Extracellular polymeric substances (EPS) production was also reduced by approx 94% with 10 J/cm2 of light dose. CLSM images showed that the thickness of biofilms were reduced from >30 µm to <5 µm after treatment with curcumin followed by 10 J/cm2 of light irradiation. Curcumin showed better bacteriostatic activity than bactericidal activity. Singlet oxygen is primarily responsible for photodamage and cytotoxic reactions caused by curcumin-mediated APDT. Genes involved in quorum sensing (QS) pathway was also found to be inhibited after APDT. Curcumin with 5 J/cm2 light inhibits QS genes and on increasing light dose i.e10 J/cm2, we found a drastic reduction in gene expression. CONCLUSION We conclude that the curcumin mediated APDT inhibits biofilm formation ofP. aeruginosa through QS pathway by the action of singlet oxygen generation which in turn reduced EPS of the biofilm.