Avaliação do tempo de incubação do fotossensibilizador curcumina em Staphylococcus aureus e Pseudomonas aeruginosa na inativação fotodinâmica

Abstract

Photodynamic Therapy (PDT) has been helping medicine in treatment infectious diseases and tumors. PDT's principle is based on a photosensitizer (PS) that is photoactivated by light at specific wavelength which generates reactive oxygen species that induces cell death and/or microorganism inactivation (PDI - photodynamic inactivation). The optimum incubation time of the photosensitizer, whereas the structural and metabolic differences of each microorganism, is important for the more efficient effect of PDI. Curcumin, being a natural PS, has been gaining ground in scientific research and has shown satisfactory results in microbiological control when associated with PDI, but there are no studies on the influence of incubation time of the PS with the bacterial cell. The present study aimed to evaluate the incubation time of curcumin on PS PDI and can therefore assist in determining future research the perfect time to contact the PS in bacteria of different wall compositions: Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa). Samples of microorganisms were cultured in TSB broth (Triptic Soy Broth) and incubated at 37 °C for 24 hours. The PS was solubilized in dimethylsulfoxide (DMSO) to achieve concentrations of 20 mM stock, subsequently diluted to obtain the final concentrations. Light source was used at a wavelength of 460nm, and final dose of 30 J/cm2. After the incubations with the FS and irradiation decimal dilutions of the samples were plated on TSA medium (Triptic Soy Agar) and incubated at 37 °C for 48 hours, and the counts performed. The PDI decreased approximately 7 logs S. aureus at a concentration of 1μM with incubation time of 30 minutes, while for P. aeruginosa was reduced by 2 logs with a maximum concentration of 50 μM with the same incubation time. Tests were conducted where PS withdrawing means before illumination, but the process was not found reductions as those obtained without the procedure. In general, the best incubation time was 30 minutes in all concentrations and for both microorganisms.