Investigação in vitro de parâmetros da terapia fotodinâmica antimicrobiana aplicada a Staphylococcus aureus

Abstract

The Photodynamic Therapy has developed mainly for anticancer treatments, however, new applications of this technique are becoming devoted against the action of microorganisms. In this case it is termed as Photodynamic Inactivation (PDI) or Antimicrobial Photodynamic Therapy (aPDT) and is gaining growing importance on the treatment of certain pathologies. Over the past years it was found that some bacteria were creating resistance to certain antibiotics, which is a serious problem, as it leads to increasing applied doses of the drug or to associated use with other techniques to try to combat the microorganism action. In turn,in a important advantage of aPDT for the treatment of infections is due to possibility of inactivating resistant strains in comparison to conventional treatments. The mechanism of action of aPDT occurs when a given photosensitizer is excited by a light source in a wavelength resonant to its absorption band in the presence of a substrate, such as oxygen. A reaction chain begins forming highly reactive chemical species with short life, such as singlet oxygen and free radicals, which can cause serious damage to microorganism due to the irreversible oxidation of cellular components. Trying to observe the inactivation of Staphylococcus aureus by means of aPDT, using a curcumin-based salt as the photosensitizer, experimental protocols, whose aim was to reproduce the optimal conditions which more prevented the growth of the microorganism, were tested. The tested food for this study was the rennet cheese, which is a component of the diet of the Northeastern Brazilian population and can to be often a reservoir of proliferation for the bacteria. The experiment was performed in triplicate, in vitro and in loco being divided into experimental groups. It was used several different powers to irradiate the samples at times of 5, 10, 15, 20 and 30 min respectively with LED light at 450 nm. The powers used were of 151 mW (P1), 204 mW (P2) e 258 mW (P3), and after the best illumination times were chosen, the light doses used were of 13 j/cm²; 16 j/cm²; 78 j/cm²; 98 j/cm². Very expressive results were obtained for all tested doses, attaining an inhibition above 80% when comparing the CONTROL group with the PDT group.