In Vitro Evaluation of the Antibacterial Effect of Photodynamic Therapy with Methylene Blue

ABSTRACT

Abstract Objective: To evaluate, in vitro, the effect of photodynamic therapy (PDT) compared to laser therapy and the use of a photosensitizer alone. Material and Methods: The following therapies were used PDT, laser therapy and photosensitizer alone. For PDT, methylene blue (MB) at different concentrations and red laser InGaAlP 660nm were used. For the use of low-power laser (LPL) alone, red laser InGaAlP 660 nm and infrared laser AsGaAl, 830 nm, both in continuous emission were used. Standard ATCC strains of Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) species were used. The antibacterial effect of PDT was quantified by the diameter of the inhibition halos. Results: PDT (LPL 660 nm, 320 J/cm2) with MB at concentration of 50 µg/mL showed antibacterial efficacy only when tested against S. aureus and E. coli strains, as well as with the isolated use of MB at the same concentration. Using LPL alone, whether red or infrared, with different dosimetry, no antibacterial effect was observed. In none of the therapeutic modalities used, P. aeruginosa inactivation was observed. Conclusion: Antibacterial effects of PDT (LPL 660 nm + MB 50 µg/mL) were observed for S. aureus and E. coli, as well as with the isolated use of MB (50 µg/mL). For P. aeruginosa, no antibacterial effect with any of the protocols recommended in the study was observed.