Antimicrobial photodynamic inactivation mediated by methylene blue: Analysis of inactivation kinetics and biochemical mechanisms

• Autor(a) principal: Sabino, Caetano Padial
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/9/9136/tde-05082021-094159/
• topic: Azul de Metileno; Bactéria; Fotoinativação; Fotoquimioterapia; Fungo; Resistência bacteriana; Terapia fotodinâmica antimicrobiana (TFDA)

The widespread use of antimicrobial chemotherapy in medicine and livestock production imposed an evolutive selection of drug-resistant strains worldwide. As a result, the effectiveness of our current antimicrobial armamentarium is constantly being reduced to alarming levels. Therefore, novel antimicrobial therapeutic strategies are urgently needed. Antimicrobial photodynamic therapy (APDT) comes to this scenario as a powerful tool to counteract the emergence of microbial drug-resistance. Its mechanisms of action are based on simultaneous oxidative damage of multiple targets and, therefore, it is much less likely to allow any type of microbial resistance. Therefore, the objectives of this study were focused into establishing 1) a mathematical tool to allow precise analysis of microbial photoinactivation; 2) a broad analysis of APDT effectiveness against global priority drug-resistant pathogens; 3) inhibition of ßlactamase enzymes; and 4) how the biochemical mechanisms of APDT avoid emergence of resistance. The main results obtained through the investigation led by this thesis were divided into 4 scientific articles regarding each of the above-mentioned objectives. In summary, we discovered that 1) a power-law function can precisely fit all microbial inactivation kinetics data and provide insightful information of tolerance factors and lethal doses; 2) there is no correlation between drug-resistance and APDT sensitivity, i.e., extensively drug resistant microorganisms are killed in the same kinetics as drug-sensitive controls; 3) β-lactamases are very sensitive to photodynamic inhibition; 4) biochemical mechanisms of APDT promote oxidative damages to external cell membranes, DNA and proteins whereas the main cause of microbial death seems to be directly associated with protein degradation. Thus, we conclude that APDT is effective against a broad-spectrum of pathogens and has minimum chances of promoting resistance mechanisms.