Aplicação da terapia fotodinâmica com uso do LED e azul de metileno em streptococcus mutans na presença de glicose - estudo in vitro

Abstract

Streptococcus mutans is a microorganism closely associated with tooth decay. Its cariogenic properties are regulated by many genes involved in essential metabolic pathways: microbial adhesion, biofilm formation, extracellular polysaccharide synthesis, carbohydrate uptake and tolerance to acid. When in the presence of glucose, the bacterium activates membrane receptors to activate transport pumps to increase glucose uptake. This process may facilitate the entry of photosensitizer into the cell. Photodynamic therapy involves incorporation of a photosensitizer (FS) into the cellular cytoplasm followed by irradiation with light, resulting in cell death. This work aims to investigate the antimicrobial action of photodynamic therapy on S. mutans in the presence of glucose. In this work, S. mutans ATCC 25175 was cultured in microaerophilic agar in brain and heart infusion (BHI) incubated at 37 ° C for 48 hours. The inoculates were prepared by collecting pure colonies that were suspended in phosphate buffered saline (PBS) with and without 50 mM of glucose. Methylene blue FS (AM) was added to the suspension giving the final concentration of 100 μM. Six groups were used: (control group, irradiated group with LED without FS, FS group without irradiation, and PDT groups). The irradiation times of the PDT group were 30, 60 and 120 seconds. The biofilm experiments used the same parameters (50 mM glucose, 100 μM AM), but the irradiation times were 60, 120, 240, 360 and 480 seconds. The Control, LED and FS groups did not present significant differences (P> 0.5) with and without glucose, or suspension and in biofilm. After 2 min of irradiation without glucose, we observed a reduction of 100% of bacteria, while there was no microbial reduction in the presence of glucose. In biofilm, there was also less photodynamic effect in the presence of glucose. The higher the radiant exposure, the greater the inactivation of S. mutans. We can conclude that PDT is a viable solution for inactivation of S. mutans, and that in the presence of glucose delays the inactivation of bacteria. The greater the radiant exposure, the greater the inactivation of S. mutans.