understand how the lung environment affects colistin treatment efficacy and to develop new therapeutic strategies to improve patient outcomes

囊性纤维化(CF)影响着英国的10,000人。早期死亡是这种疾病的特征，主要是由慢性肺部感染和炎症性气道壁损伤引起的。成年后，60%的患者长期感染革兰氏阴性菌，即铜绿假单胞菌(PA)。目前的治疗是有限的，一旦感染是慢性的，最好的方法就是‘抑制’细菌负荷，通常是吸入抗菌剂。PA感染战略研究中心是由Jane C Davies教授建立的，致力于提高对致病机制和治疗方法的了解。它通过高级临床学者与皇家Brompton医院的CF诊所合作，这是欧洲最大的诊所之一，支持了该计划强烈的翻译重点。正在开发的新抗生素的狭窄管道意味着迫切需要努力提高现有药物的疗效。Colistin是INCF中最常用的多粘菌素类抗生素，用于控制慢性铜绿假单胞菌感染。不幸的是，虽然粘菌素通常有效地抑制感染，但一旦慢性感染确定，它几乎永远不能从肺部清除铜绿假单胞菌。静脉注射粘菌素也被用作严重疾病的最后手段，因此，出现耐药的拓扑粘菌素抗生素是一个日益令人担忧的问题。由于对抗生素的作用模式缺乏了解，以及缺乏关于宿主环境对细菌敏感性的影响的知识，提高粘菌素疗效的努力一直受到阻碍。总部设在MRC分子细菌学和感染中心的爱德华兹实验室最近的研究表明，粘菌素的靶标是外膜和细胞膜中的内毒素，导致细菌溶解和杀死(Sabennis等人，2019年)。我们还发现，由于脂多糖修饰酶的移动粘菌素耐药(MCR)家族(Liu等人，2016)导致的粘菌素耐药性是由于细胞质膜上的内毒素修饰(Sabius等人，2019)。我们利用这一信息开发了一种联合治疗方法来增强结肠素活性。我们发现，实验抗生素murepaadin引起铜绿假单胞菌细胞膜内毒素的积聚，使该细菌对粘菌素介导的杀灭敏感1000倍。考虑到与呼吸道狭窄和粘液堵塞相关的吸入剂在呼吸道沉积中的地理异质性，以及由此导致的药物浓度的差异，提高低药物浓度疗效的成功方法可能会产生直接的临床影响。这项工作的关键下一步是确定宿主环境如何影响LPS的加工和运输，我们假设这将对粘菌素易感性产生重大影响，从而影响治疗结果。例如，在这项工作中，我们发现接触粘菌素的细菌释放的内毒素可以隔离抗生素，使其无效。我们还发现，人血清的存在使铜绿假单胞菌对粘菌素具有耐受性。这些发现表明粘菌素的疗效受到体内环境的影响，但这需要进一步的研究。

Cystic fibrosis (CF) affects >10,000 people in the UK. Early mortality characterises the disease, largelydriven by chronic lung infection and inflammatory airway wall damage. By adulthood >60% patientsare chronically infected with the Gram-negative organism, Pseudomonas aeruginosa (Pa). Currenttherapy is limited, and once infection is chronic, the best that can be achieved is 'suppression' ofbacterial load, usually with inhaled antimicrobials. The Strategic Research Centre for Pa infectionwas established by Prof Jane C Davies, with a focus on improving understanding of pathogenicmechanisms and therapies. Its partnership with the Royal Brompton Hospital's CF clinic, one of thelargest in Europe, through senior clinical academics, underpins the strong translational focus of theprogramme. The narrow pipeline of new antibiotics under development means that work to improveefficacy of existing agents is urgently needed.Colistin is the polymyxin antibiotic used most commonly to control chronic P. aeruginosa infection inCF. Unfortunately, whilst colistin is usually effective in suppressing infection, it is almost never ableto clear P. aeruginosa from the lungs once chronic infection is established. Intravenous colistin isalso used as a 'last-resort' agent in severe disease, and thus, the emergence of resistance topolymyxin antibiotics is a growing concern. Efforts to improve colistin efficacy have been hamperedby a poor understanding of the antibiotic's mode of action and the lack of knowledge around theimpact that the host environment has on bacterial susceptibility. Recent work from the Edwards lab,based in the MRC Centre for Molecular Bacteriology and Infection, has revealed that colistin targetsLPS in both the outer and cytoplasmic membranes, leading to bacterial lysis and killing (Sabnis et al.,2019). We have also shown that colistin resistance due to the mobile colistin resistance (MCR) familyof LPS modifying enzymes (Liu et al., 2016) is due to modification of LPS at the cytoplasmicmembrane (Sabnis et al., 2019).We exploited this information to develop a combination therapeutic approach to enhance colistinactivity. We found that the experimental antibiotic murepavadin caused the accumulation of LPS inthe cytoplasmic membrane of P. aeruginosa, which sensitised the bacterium >1000-fold to colistin mediated killing. Given the geographical heterogeneity in airway deposition of inhaled agentsrelated to airway narrowing and mucus plugging, and the resulting variability in drug concentrations,successful approaches to enhance efficacy of lower drug concentrations could have direct clinicalimpact.The crucial next step in this work is to determine how the host environment influences LPSprocessing and transport, which we hypothesise will have significant effects on colistin susceptibilityand therefore treatment outcomes. For example, during this work, we found that LPS released bybacteria exposed to colistin can sequester the antibiotic, rendering it ineffective. We also found thatthe presence of human serum renders P. aeruginosa tolerant of colistin. These findings indicate thatcolistin efficacy is affected by the in vivo environment, but this requires further investigation.