Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 15 3 2018 06 13 169 177 EN Maryam Pourhajibagher Researcher, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Nasim Chiniforush Researcher, Laser Research Center of Dentistry, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Abbas Monzavi Professor, Laser Research Center of Dentistry, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Prosthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Hamidreza Barikani Researcher, Dental Implant Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Mohammad Moein Monzavi Dentist, Private Practice, Tehran, Iran Shaghayegh Sobhani Dentist, Private Practice, Tehran, Iran Sima Shahbi Professor, Laser Research Center of Dentistry, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Dental Biomaterials, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Abbas Bahador Associate Professor, Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran 2017 11 12 2018 02 06 Objectives: Periodontitis is an inflammation of periodontal tissues that is caused by the biofilm of periodontal pathogens. Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) is an opportunistic periodontopathogen that can be the cause of periodontal diseases via fimbriae as a virulence factor. In this study, we aimed to determine the expression level of A. actinomycetemcomitans rcpA gene as a virulence factor associated with biofilm formation after antimicrobial photodynamic therapy (aPDT) as a relatively new therapeutic modality. Materials and Methods: To determine sub-lethal doses of aPDT against A. actinomycetemcomitans ATCC 33384 strain, we used curcumin (CUR) as a photosensitizer at a final concentration of 40 µmol/ml, which was excited with a light-emitting diode (LED) at the wavelength of 450 nm. Quantitative real-time polymerase chain reaction (qRT-PCR) was then applied to monitor rcpA gene expression in A. actinomycetemcomitans. Results: 10-40 μmol/ml of CUR caused a significant reduction in the growth of A. actinomycetemcomitans compared to control group (P<0.05). Also, the cell viability of A. actinomycetemcomitans was significantly decreased after more than four minutes of LED irradiation. Therefore, the sub-lethal dose of aPDT against A. actinomycetemcomitans was 5 μmol/ml of CUR with three minutes of LED irradiation at a fluency of 180-240 J/cm2, which reduced the expression of the rcpA gene by approximately 8.5-fold. Conclusions: aPDT with CUR leads to decreased cell survival and virulence of A. actinomycetemcomitans. Thus, CUR-aPDT can be used as an alternative approach for the successful treatment of periodontitis in vivo. https://fid.tums.ac.ir/index.php/fid/article/view/2231 https://fid.tums.ac.ir/index.php/fid/article/download/2231/1006