Copyright@ Arash Mohammadi Tofigh | Biomed J Sci & Tech Res | BJSTR. MS.ID.006060. 29781 Research Article ISSN: 2574 -1241 Effects of Photodynamic Therapy on Staphylococcus Aureus Viability and Staphylocoagulase Activity, an Ex-Vivo Trial Arash Mohammadi Tofigh 1 * and Mersedeh Karvandi 2 1 Associate Professor of Surgery, Laser Application in Medical Sciences Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2 Associate Professor of Cardiology, Laser Application in Medical Sciences Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran *Corresponding author: Arash Mohammadi Tofigh, Associate Professor of Surgery, Laser Application in Medical Sciences Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran DOI: 10.26717/BJSTR.2021.37.006060 ARTICLE INFO ABSTRACT Introduction: This study was designed to assess photodynamic treatment (PDT) effects on biological inhibition of Staphylococcus aureus (S. aureus). It is mainly focused on reducing the activity of Staphylocoagulase (SC), an essential product of the bacteria. The PDT effects were evaluated on the inhibition of the bacteria’s enzymatic activity and total bacterial count (viability). Methods: A 650nm wavelength diode laser was used with 100mW output power and 2 minutes of exposure time. We used 50, 100, 150, and 200 μg/ml MB dilutions as a photosensitizer. The viability of bacteria after and before laser treatment was calculated using single plate-serial dilution spotting methods. The activity of staphylocoagulase was detected by incubating it with human plasma and assessment of crude-substrate interaction. Results: Our findings approved that 2 minutes’ irradiation of S. aureus with 650nm diode laser alone results in rising total cell number and SC activity while photosensitizing with 150 μg/ml concentration of MB results in significant inhibition of SC activity, compared with other groups. Conclusion: The optimal concentration of MB dye as a photosensitizer for maximum penetration to the intracellular bacterial structure, resulting in reactive oxygen species production inside and outside the bacterial cell’s plasma membrane, is 150 μg/ml. Using a laser wavelength of 650 nm along with this concentration of MB reduces the activity of SC. Abbreviations: S. aureus: Staphylococcus aureus; PDT: Photodynamic Treatment; SC: Staphylocoagulase; MB: Methylene Blue; CFU: Colony Forming Unite; MRSA: Methicil- lin-Resistant Staphylococcus aureus; PCAM: Prothrombin Conformational Activation Mechanism; APDT: Antimicrobial Photodynamic Treatment; ROS: Reactive Oxygen Spe- cies; IRA: S. aureus with laser irradiation; 50PDY: S. aureus suspension in 50 μg/ml MB and laser irradiation; 100PDY: S. aureus suspension in 100 μg/ml MB and laser irradi- ation; 150 PDY: S. aureus; suspension in 150 μg/ml MB and laser irradiation; 200PDY: S. aureus suspension in 200 μg/ml MB and laser irradiation; CHB: Casein Hydrolysate Broth; CHM: Casein Hydrolysate Medium ; SP-SDS: Single; Plate-Sequential Dilution Spotting ; OD: Optical Density ; DW: Distilled Water ; LLLT: Low-Level Laser Treatment; PS: Photosensitizer; SOD: Superoxide Dismutase Received: July 24, 2021 Published: August 04, 2021 Citation: Arash Mohammadi Tofigh and Mersedeh Karvandi. Effects of Photody- namic Therapy on Staphylococcus Aureus Viability and Staphylocoagulase Activity, an Ex-Vivo Trial. Biomed J Sci & Tech Res 37(5)-2021. BJSTR. MS.ID.006060. Keywords: Photodynamic Therapy; Staphylocoagulase; Laser; Enzyme activi- ty; Methylene blue