Açucares e seus efeitos no comportamento antimicrobiano da terapia fotodinâmica em Streptococcus mutans

Abstract

Streptococcus mutans (S. mutans) are Gram-positive bacteria that can be found in the oral cavity, larynx and intestine. In the presence of sucrose, fructose and glucose, S. mutans are able to form EPS, which are the main constituents of the matrix present in cariogenic biofilms. Mannitol is found naturally in plants, bacteria, algae and fungi, but S. mutans is not able to metabolize mannitol, which is used as a non-cariogenic substitute for sugar. In the presence of sugars, S. mutans activates membrane receptors by stimulating transport pumps, thus increasing glucose uptake. Verapamil, in addition to a calcium channel blocker, also acts as an inhibitor to several efflux pumps. Inactivating this pump in apoptotic cells increases the toxicity potential of PDT. Photodynamic therapy consists of incorporation of a photosensitizer by the cellular cytoplasm, followed by irradiation with visible light, a process that results in cell death. The objective of this work was to investigate the effect that sugars have on the antimicrobial behavior of photodynamic therapy in Streptococcus mutans (S. mutans). We used S. mutans (ATCC 25175) that was cultured in microaerophilic agar in brain and heart infusion (BHI) incubated at 37 ° C for 48 h. Bacterial inoculate was prepared by collecting pure colonies that were suspended in phosphate-saline buffered solution (PBS) in the presence and absence of glucose and mannitol. Methylene blue (AM) photosensitizer (FS) was added to the suspension, resulting in a final concentration of 100 µM. Verapamil was used as a blocker of efflux pumps. The experiments were carried out in the presence of glucose, mannitol and verapamil, with each experiment divided into the following groups: control, LED without FS and PDT at times 0, 60 and 120 s. The Control, LED and FS groups did not show significant differences (P> 0.5) in the presence and absence of sugars as well as Verapamil. In the PDT groups with AM and AM + Verapamil with 2 min. of irradiation a microbial reduction of almost 5 logs can be observed. In those performed with glucose, the microbial reduction was 3 logs. Experiments performed with mannitol and mannitol + Verapamil with a microbial reduction of only 2 logs can be observed. With optical absorption spectroscopy, it was possible to observe that both in the presence and absence of sugars the absorption of AM by S. mutans was the same, as well as the experiments in which the amount of ROS being formed was evaluated was the same for the groups used. We can conclude that PDT is a viable solution for S. mutans inactivation and that in the presence of sugars we have a delay in microbial death.