Antibiotic-resistant Pseudomonas aeruginosa infections are the primary cause of mortality in people with cystic fibrosis (CF). Yet, it has only recently become appreciated that resistance mutations can also increase P. aeruginosa virulence, even in the absence of antibiotics. Moreover, the mechanisms by which resistance mutations increase virulence are poorly understood. In this study we tested the hypothesis that mutations affecting efflux pumps can directly increase P. aeruginosa virulence. Using genetics, physiological assays, and model infections, we show that efflux pump mutations can increase virulence. Mutations of the mexEF efflux pump system increased swarming, rhamnolipid production, and lethality in a mouse infection model, while mutations in mexR that increased expression of the mexAB-oprM efflux system increased virulence during an acute murine lung infection without affecting swarming or rhamnolipid gene expression. Finally, we show that an efflux pump inhibitor, which represents a proposed novel treatment approach for P. aeruginosa, increased rhamnolipid gene expression in a dose-dependent manner. This finding is important because rhamnolipids are key virulence factors involved in dissemination through epithelial barriers and cause neutrophil necrosis. Together, these data show how current and proposed future anti-Pseudomonal treatments may unintentionally make infections worse by increasing virulence. Therefore, treatments that target efflux should be pursued with caution.

中文翻译：

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铜绿假单胞菌 mexR 和 mexEF 抗生素外排泵变体表现出增加的毒力

耐抗生素铜绿假单胞菌感染是囊性纤维化 (CF) 患者死亡的主要原因。然而，直到最近才认识到耐药性突变也可以增加铜绿假单胞菌的毒力，即使在没有抗生素的情况下也是如此。此外，人们对耐药性突变增加毒力的机制知之甚少。在这项研究中，我们测试了影响外排泵的突变可以直接增加铜绿假单胞菌毒力的假设。使用遗传学、生理学分析和模型感染，我们表明外排泵突变可以增加毒力。mexEF的突变在小鼠感染模型中，外排泵系统增加了集群、鼠李糖脂的产生和致死率，而增加mexAB-oprM外排系统表达的mexR突变增加了急性鼠肺感染期间的毒力，而不影响集群或鼠李糖脂基因的表达。最后，我们展示了一种外排泵抑制剂，它代表了铜绿假单胞菌的一种新的治疗方法，以剂量依赖性方式增加鼠李糖脂基因表达。这一发现很重要，因为鼠李糖脂是参与通过上皮屏障传播并导致中性粒细胞坏死的关键毒力因子。总之，这些数据显示了当前和拟议的未来抗假单胞菌治疗如何通过增加毒力无意中使感染恶化。因此，应谨慎进行针对外排的治疗。