Antimicrobial photodynamic inactivation (aPDI) uses photosensitizers (PSs) and harmless visible light to generate reactive oxygen species (ROS) and kill microbes. Multidrug efflux systems can moderate the phototoxic effects of PSs by expelling the compounds from cells. We hypothesized that increasing intracellular concentrations of PSs by inhibiting efflux with a covalently attached efflux pump inhibitor (EPI) would enhance bacterial cell phototoxicity and reduce exposure of neighboring host cells to damaging ROS. In this study, we tested the hypothesis by linking NorA EPIs to methylene blue (MB) and examining the photoantimicrobial activity of the EPI–MB hybrids against the human pathogen methicillin-resistant Staphylococcus aureus (MRSA). Photochemical/photophysical and in vitro microbiological evaluation of 16 hybrids carrying four different NorA EPIs attached to MB via four linker types identified INF55-(Ac)en–MB 12 as a lead. Compound 12 showed increased uptake into S. aureus cells and enhanced aPDI activity and wound healing effects (relative to MB) in a murine model of an abrasion wound infected by MRSA. The study supports a new approach for treating localized multidrug-resistant MRSA infections and paves the way for wider exploration of the EPI–PS hybrid strategy in aPDI.

中文翻译：

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附加诺拉外排泵抑制剂INF55至耐甲氧西林的亚甲基蓝增强抗菌光动力灭活金黄色葡萄球菌在体外和在体内

抗菌光动力灭活（aPDI）使用光敏剂（PSs）和无害的可见光生成活性氧（ROS）并杀死微生物。多药外排系统可通过将化合物从细胞中排出来减轻PS的光毒性作用。我们假设通过用共价连接的外排泵抑制剂（EPI）抑制外排来增加PSs的细胞内浓度会增强细菌细胞的光毒性，并减少邻近宿主细胞暴露于有害ROS的风险。在这项研究中，我们通过将NorA EPI连接至亚甲基蓝（MB）并检验了EPI-MB杂种对人类病原体耐甲氧西林金黄色葡萄球菌（MRSA）的光抗菌活性，从而验证了这一假设。光化学/光物理和体外对通过四种连接子连接到MB的带有四个不同NorA EPI的16个杂种进行的微生物学评估确定，INF55-（Ac）en-MB 12为先导。在被MRSA感染的擦伤伤口的小鼠模型中，化合物12显示出增加了对金黄色葡萄球菌细胞的摄取并增强了aPDI活性和伤口愈合效果（相对于MB）。该研究支持了一种用于治疗局部多药耐药性MRSA感染的新方法，并为在aPDI中更广泛地探索EPI-PS混合策略铺平了道路。