Dados do Trabalho

Título

Antimicrobial Photodynamic Therapy (APDT) Using Cationic Porphyrin and Zinc-porphyrin Photosensitizers

Introdução

Antimicrobial Photodynamic Therapy (APDT) emerges as an attractive alternative to the use of antibiotics in the treatment of microbial infections, based on oxidative processes generated by photosensitizers (PS) stimulated by light.

Objetivo (s)

To investigate how the structural differences in cationic porphyrin compounds influence the photodynamic action in the inactivation of Gram positive and negative bacteria and microalgae.

Material e Métodos

The cationic porphyrins meso-Methylpyridinium-Porphyrin (P1) and meso-Benzylpyridinium-Porphyrin (P2) and their respective metallic Zn(II) complexes (ZnP1 and ZnP2) were used. S. aureus, E. coli and P. aeruginosa were grown in LB medium and P. zopfii was grown in BHI medium, at 37ºC overnight and then adjusted to E7 – E8 CFU/mL. Photoinactivation was performed with suspensions of microorganisms previously incubated with photosensitizers and then washed with PBS. The samples were irradiated with 405 or 450 nm laser 200-300 mW, under agitation. Photoinactivation experiments were compared with respective controls. This study was submitted to the ethics committee: CEP-ICB nº 1014/2019.

Resultados e Conclusão

Results: Zinc derivatives (ZnP) proved to be the most effective photosensitizers for all microorganisms investigated, requiring lower concentrations and shorter irradiation times to observe total inactivation. Particularly relevant are the results for the photoinactivation of the Gram negative P. aeruginosa and E. coli bacteria, which at ZnP concentrations of the order of 5E-7 – 5E-6 M, result in inactivation with irradiation times of 60 – 90 s. S. aureus was the microorganism most sensitive to the action of the PS since concentrations of the order of 1E-8 M of PS produce total inactivation within irradiation times of 30 – 60 s. P1 (5E-7 M) was less effective in inactivating P. zopfii with a drop of 4log in 90 s irradiation; contrasting result is obtained with their zin-complex ZnP1 at very low concentration (5E-9 M)  with total inactivation in 150 s. ZnP2 and P2 (both 5E-8 M) result in complete inactivation in irradiation times 30 – 60 s respectively. Conclusions: The cationic porphyrinic PS are extremely effective in the in vitro inactivation of microorganisms at low concentrations with reduced irradiation times, particularly in the case of ZnP and the presence of the benzyl-pyridinium substituent, indicating that these structural characteristics result in a preferential interaction with microorganisms leading to the inactivation process.

Palavras Chave

Antimicrobial Photodynamic Therapy; Cationic Porphyrin Photosensitizers; Gram Negative and Positive Bacteria Photoinactivation; Microalgae Photoinactivation