Photodynamic inactivation of KPC-producing Klebsiella pneumoniae difficult-to-treat resistance (DTR) by a cationic porphyrin

The 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 mu M under an irradiance of 314 +/- 11 mW/cm(2), delivering a total light dose of 189 J/cm(2). At the same concentration, bacterial suspensions exposed to a lower irradiance of 107 +/- 7 mW/cm(2) achieved a > 99.997 % reduction in viability with a lethal light dose of 51.4 J/cm(2). 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.