Resistance of bacteria to antibiotics is a public health concern worldwide due to the increasing failure of standard antibiotic therapies. Antimicrobial photodynamic inactivation (aPDI) is a promising non-antibiotic alternative for treating localized bacterial infections that uses non-toxic photosensitizers and harmless visible light to produce reactive oxygen species and kill microbes. Phenothiazinium photosensitizers like methylene blue (MB) and toluidine blue O are hydrophobic cations that are naturally expelled from bacterial cells by multidrug efflux pumps, which reduces their effectiveness. We recently reported the discovery of a NorA efflux pump inhibitor-methylene blue (EPI-MB) hybrid compound INF55-(Ac)en–MB that shows enhanced photodynamic inactivation of the Gram-positive bacterium methicillin-resistant Staphylococcus aureus (MRSA) relative to MB, both in vitro and in vivo. Here, we report the surprising observation that INF55-(Ac)en–MB and two related hybrids bearing the NorA efflux pump inhibitors INF55 and INF271 also show enhanced aPDI activity in vitro (relative to MB) against the Gram-negative bacteria Escherichia coli and Acinetobacter baumannii, despite neither species expressing the NorA pump. Two of the hybrids showed superior effects to MB in murine aPDI infection models. The findings motivate wider exploration of aPDI with EPI-MB hybrids against Gram-negative pathogens and more detailed studies into the molecular mechanisms underpinning their activity.

由于标准抗生素疗法的失败越来越多，细菌对抗生素的耐药性已成为全球公共卫生关注的问题。抗菌光动力灭活（aPDI）是一种有前途的非抗生素替代品，可用于治疗局部细菌感染，这种细菌使用无毒的光敏剂和无害的可见光产生活性氧并杀死微生物。亚甲基蓝（MB）和甲苯胺蓝O等吩噻嗪鎓光敏剂是疏水性阳离子，可通过多药外排泵从细菌细胞中自然排出，从而降低了它们的功效。我们最近报道了发现NorA外排泵抑制剂-亚甲基蓝（EPI-MB）杂合化合物INF55-（Ac）en-MB的发现，该化合物显示出对革兰氏阳性细菌耐甲氧西林的增强的光动力失活相对于MB的金黄色葡萄球菌（MRSA），在体内和体外均如此。在这里，我们报告了令人惊讶的观察结果，即INF55-（Ac）en-MB和两个带有NorA外排泵抑制剂INF55和INF271的相关杂种在体外（相对于MB）还显示出对革兰氏阴性细菌大肠杆菌和大肠杆菌的增强的aPDI活性。鲍曼不动杆菌，尽管没有一个物种表达NorA泵。其中两个杂种在鼠aPDI感染模型中显示出比MB更好的效果。这些发现促使人们对具有EPI-MB杂种的革兰氏阴性病原体对aPDI进行了更广泛的探索，并对其基础分子机制进行了更详细的研究。