Croconaine and squaraine dyes: their role as photosensitizers in antimicrobial photodynamic therapy

• Autor(a) principal: Martins, Bruno
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10348/11009
• topic: Antimicrobial photodynamic therapy; squaraine dyes

Wounds represent a location in the organism of possible bacteria contamination. These are part of the skin's natural microbiota, but in reduced quantities. A high concentration of bacteria on the wound location can lead to the development of chronic wounds or infections. In the past few years, the excessive use of antibiotics has led to the development of several bacterial multirresistance mechanisms, which means it is necessary to develop alternative therapies in hopes to ease this problematic. Bacterial multiresistance limits treatment options against bacteria, which possess a high epidemic dissemination capacity that can lead to serious infections. In this study, croconaine and squaraine dyes were synthesized, spectroscopically characterized and their phototherapeutic effect was studied when irradiating bacteria together with dye solutions (640 nm and 700 nm, with concentrations of 0.01, 0.1, 1, 2.5 and 10 µM) to evaluate their antibacterial ability. The bacteria used in this study originated from polymicrobial infections from two patients from different CHTMAD (Centro Hospitalar de Trás-os-Montes e Alto Douro) services, posteriorly catalogued to the MJMC collection (588, 589, 590, 602, 603, 604). Two different control bacteria were used: an S. aureus CECT 976 and an E. coli CECT 434; a Gram-positive and a Gramnegative bacterium, respectively. The studied bacteria showed a typical behavior for Gram-positive and Gramnegative bacteria, whereas the first ones showed a higher dye permeability through their cell wall. This permeability can be enhanced by adding agents that could favor the disruption of their cell walls. The synthesized dyes showed a satisfactory level of purity. However, these showed to be difficult to synthesized due to the necessary care during the synthesis process. The obtained results revealed that the synthesized dyes showed some antimicrobial photoinactivation potential, which can be improved with structural changes, enhancing their phototherapeutic effect.