2025-09-022025-09-022025FREITAS, Alysson Benite de et al. Photodynamic inactivation of KPC-producing Klebsiella pneumoniae difficult-to-treat resistance (DTR) by a cationic porphyrin. Journal of Photochemistry and Photobiology B: biology, Lausanne, v. 265, e113133, 2025. DOI: 10.1016/j.jphotobiol.2025.113133. Disponível em: https://www.sciencedirect.com/science/article/pii/S1011134425000363?via%3Dihub. Acesso em: 1 set. 2025.1011-1344e- 1873-2682https://www.sciencedirect.com/science/article/pii/S1011134425000363?via%3DihubThe global rise of difficult-to-treat resistance (DTR) bacteria, such as Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae (KPC-Kp), poses a critical challenge in controlling infections and curbing the spread of antimicrobial resistance genes. Antimicrobial photodynamic inactivation (aPDI) offers a promising alternative to traditional antimicrobials by effectively targeting extensively drug-resistant pathogens and mitigating antimicrobial resistance. This study investigated the in vitro photodynamic efficacy of the cationic porphyrin 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) against planktonic cultures of KPC-Kp. The minimum effective concentration (MEC) of TMPyP for significant photodynamic activity was determined to be 0.8 μM under an irradiance of 314 ± 11 mW/cm2, delivering a total light dose of 189 J/cm2. At the same concentration, bacterial suspensions exposed to a lower irradiance of 107 ± 7 mW/cm2 achieved a > 99.997 % reduction in viability with a lethal light dose of 51.4 J/cm2. Scanning electron microscopy (SEM) revealed oxidative damage to the bacterial cell wall induced by aPDI. Hemolysis assays confirmed the safety of TMPyP, with no significant cytotoxicity or photocytotoxicity observed, and a selectivity index (SI) greater than 8, indicating a favorable therapeutic window. These findings underscore the potential of TMPyP-based aPDI as a therapeutic strategy to combat KPC-Kp infections. Further studies are warranted to explore its clinical applications and optimize treatment protocols for DTR bacterial infections.engAcesso Restrito5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP)Antimicrobial photodynamic inactivation (aPDI)Difficult-to-treat resistance (DTR) bacteriaK. pneumoniae carbapenemase producing K. pneumoniae (KPC-Kp)Lethal doseArtigo10.1016/j.jphotobiol.2025.113133