Induced Protoporphyrin IX Accumulation by the δ-Aminolevulinic Acid in Bacteria and its Potential Use in the Photodynamic Therapy

摘要

The increasing incident of resistant strains to antibiotic has encouraged the searchof new antibacterial treatments, such as the photodynamic therapy. In recent years,photodynamic therapy has demonstrated being a good technology for the treatment of recurrentbacteria infection. PDT presents a hopeful approach to eliminate Gram positive and negativebacteria in immunological compromised patients. This therapy uses a laser in combination witha photosensibilizer in presence of intracellular molecular oxygen. The process generates aneffect of phototoxicity in bacterial cells. The aim of this work was to determine the in vitro conditions to accumulate PpIX in effectiveconcentrations in Staphylococcus aureus ATCC25923 and Streptococcus pyogenes, which areresponsible of human cutaneous diseases. A cellular suspension of both strains was prepared inTSB to obtain growth in Log-phase, then, the suspensions were adjusted to a final concentrationof 2.61x108 cells/mL. The strains were exposed to increasing concentrations from 0 to 160μg/mL of δ-ALA in order to determinate the concentration that induces biggestaccumulation of PpIX. PpLX was measured using the Piomelli method modified for bacteria.The concentration selected was 40 mg/mL of ALA. It was found that in basal concentration ofδ-ALA (0 μg/mL) both strains accumulated similar amount of PpIX. In concentrations 5mg/mL of δ-ALA it was observed a significant (p <0.001) increment in PpIX concentration.Finally it was realized a kinetic to determinate the optimal accumulation over the time at 0, 5,10, 15 and 30 min, and 1, 2, 4, 8, 16 and 32 h. It was found that the ideal time for PDTapplication, in both strains, was 24 h because in smaller times there was not statisticallysignificant difference. The S. aureus ATCC25923 accumulated significantly the biggestconcentration of PpIX with regard to S. pyogenes.In conclusion, it was found that the optimal conditions to apply PDT will be to expose bothstrains to 40 mg/mL of ALA and to irradiate at 24 h after the exposition.