Reza Fekrazad
Hadi Zare
Sara Mohammadi Sepahvand
Parisa Morsali

Abstract Introduction: The aim of this study is the evaluation of the effect of Antimicrobial Photodynamic Therapy with Radachlorin on Staphylococcus aureus and Escherichia coli.New windows are open in the antimicrobial field so-call Photodynamic therapy that incorporates a nonpoisonous photosensitizer (PS) with innocuous special wavelength photons to excite the PS.Methods: Two strains of bacteria used in this study were Methicillin resistant Staphylococcus aureus (ATCC ۳۳۵۹۱; PTCC ۱۷۶۴) and Escherichia coli (ATCC ۲۵۹۲۲; PTCC۱۳۹۹). Concentrations of ۰.۲ ml of Radachlorin® were applied on ۰.۲ ml of bacterial suspensions and placed in a ۴۸-well microtiter plate. The following groups were used: (I) L− PS− (no laser, no photosensitizer), (II) L−PS+ (treated only with PS), (III) L+ PS− (treated only with laser) and (IV) L+ PS+ (treated with laser and PS: photodynamic therapy group). Aliquots of bacterial suspensions were sensitized with Radachlorin® for ۱۵ minutes in the dark at room temperature and then bacterial suspensions in group III and IV were irradiated with ۲۱۰ mW (power density) and ۱۲ J/cm۲ (energy density) on continuous mode.Results: This study showed that photodynamic therapy reduces ۰.۱۴ log ۱۰ in E.Coli (group IV) and there were significant differences for group IV (P<۰.۰۱). Photodynamic therapy in S.Aureus showed ۶.۲۸ log ۱۰ colony count reduction (group IV) and there were highly significant differences in Photodynamic therapy group (P<۰.۰۰۰۱).Conclusion: Radachlorin® have bactericidal effect on S.aureus (۶.۲۸ log ۱۰) and bacteriostatic effect on E.coli (۰.۱۴ log ۱۰). Keywords: photodynamic therapy staphylococcus aureus escherichia coli