Photobiomodulation and Antimicrobial Photodynamic Influence of a 650 nm Wavelength on Staphylocoagulase and Viability of Staphylococcus aurous

Staphylococcus aureus is one of the critical pathological bacteria. This bacterium had developed a variety of genetic mutations that made it resistant to drugs and more harmful to humans. In addition, all attempts to design a specific vaccine against S. aureus have failed. Therefore, this experiment was designed as a trial for vaccine production, by using a photodynamic treatment (PDT) through partial biological inhibition. The PDT of bacteria mainly focused on reducing the activity of staphylocoagulase (SC), which has a protective feature for bacteria. This study aimed to examine the photodynamic effect of combining a specific wavelength of a laser and a certain dilution photosensitizer, methylene blue (MB) dye. The possible PDT effect on the inhibition of pathogenic enzymatic activity was predicted. This study also aimed to evaluate the inhibitory effect of PDT on the total bacterial account (viability) simultaneously with SC assay.

A 650nm wavelength diode laser was used with 100 mW output power and 2 minutes of exposure time. Dye dilutions were 50, 100, 150 and 200 μg/mL. The viability of bacteria after and before laser treatment was calculated using single plate-serial dilution spotting methods. The activity of SC was detected by using human plasma for 4 hours incubation of crude-substrate interaction.

The results revealed a significant decrease in enzyme activity and colony-forming units (CFU) after irradiating bacterial suspension with 150 g/mL MB, as well as a decline in CFU. However, irradiation with a laser alone showed a significant increase in SC activity and CFU for the same exposure time.

Besides reducing the production of SC activity, PDT significantly inhibited the viability of S. aureus. The application of MB photosensitizer at a concentration of 150 g/mL in combination with a laser wavelength of 650 nm resulted in a complete decrease in the SC activity value as well as the viability of bacteria