Antimicrobial Photodynamic Therapy with Methylene Blue and Urea in Escherichia Coli and Staphylococcus Aureus

Antimicrobial Photodynamic Therapy (aPDT) is the technique in which a photosensitizing agent (PS) in the presence of oxygen is activated by light of a specific wavelength, resonant to the PS, generating reactive oxygen species through the photodynamic process, promoting the microbial death from oxidative damage. The aim of this study was to evaluate the efficacy of aPDT with methylene blue (MB) and MB with urea (UMB) in bacteria as a proof of concept of the urea-disaggregating action on phenothiazine PS. Sterile dental diamond burs were contaminated with gram negative Escherichia coli (E. coli) and gram positive Staphylococcus aureus (S. aureus) bacteria (10 8 CFU/mL) and divided into three groups (n = 9): GMB (MB + red laser- RL), GUMB (urea +MB + RL), GC (control-without treatment). The contaminated diamond burs were immersed in tubes with aqueous solution of MB (60 µM) (GMB) or MB diluted in urea (60 µM) (GUMB). After 1 min, irradiation was performed with RL (660 nm, 100 mW, 18 J, 3 min), in contact below and above the tube. The results presented in colony forming units (CFU/ml) showed that the MB and UMB groups showed significantly greater microbial reduction than GC (p < 0.05), for all microorganisms. The microbial reduction of the group with urea (GUMB) was not superior to the group without urea (GMB). It can be concluded that aPDT with MB and UMB promoted effective antimicrobial actions, the disaggregation factor that urea has in phenothiazine PS, in this in vitro experiment, was not determinant in microorganisms in suspension.