Rethinking the barrier: How a Gram-negative bacterium alters its surface to become multidrug resistant

 描述(申请人提供)：细菌病原体利用各种分子机制在不可预测的和不利的环境条件下生存。革兰氏阴性菌经常改变其暴露在环境中的外膜，这是一个不对称的双层，由内叶甘油磷脂和必要的外叶脂寡糖(LPS)或脂多糖(LOS)组成。鲍曼不动杆菌是一种革兰氏阴性医院病原菌，由于其对抗生素产生耐药性的能力，在医疗保健环境中蓬勃发展。多药耐药鲍曼不动杆菌在过去十年中变得普遍，针对外膜基本LOS的粘菌素等最后一线抗生素越来越多地被开出用于治疗多药耐药感染。而粘菌素耐药性是 曾经很少见的情况已经不再是这样了，特别是对鲍曼不动杆菌。独特的是，鲍曼不动杆菌可以完全关闭LOS的生物合成，从而对粘菌素和许多其他常用的处方药产生抗药性。这一发现令人惊讶，因为内毒素/LOS通常是革兰氏阴性细菌生存所必需的。导致LOS缺乏症和由此产生的多药耐药表型的机制尚不清楚。这项提案的总体目标是描述和理解一种新的多药耐药机制。这项建议的具体目的是(I)了解LOS完全丧失的遗传要求和(Ii)确定LOS缺陷鲍曼不动杆菌外膜通透性障碍的特征。这项工作的完成将有助于了解内毒素/LOS在革兰氏阴性细菌中的重要性，并提供对新的多药耐药机制所需的分子机制的理解。这一提议的基础科学框架也可能导致新疗法和改进疫苗的开发。

 DESCRIPTION (provided by applicant): Bacterial pathogens exploit various molecular mechanisms to survive unpredictable and adverse environmental conditions. Gram-negative bacteria often alter their environmentally exposed outer membrane, an asymmetric bilayer consisting of inner leaflet glycerophospholipids and essential outer leaflet lipooligosaccharide (LPS) or lipopolysaccharide (LOS). Acinetobacter baumannii is a Gram-negative nosocomial pathogen that thrives in healthcare settings because of its ability to develop resistance to antibiotics. Multidrug resistant A. baumannii have become widespread over the past decade and last-line antibiotics such as colistin, which target the essential LOS in the outer membrane, have been increasingly prescribed to treat multidrug resistant infections. While colistin resistance was once rare, this is no longer the case, especially regarding A. baumannii. Uniquely, A. baumannii can completely shutdown LOS biosynthesis to develop resistance to colistin and many other commonly prescribed antibiotics. This finding is surprising since LPS/LOS are typically essential for Gram-negative bacterial viability. Mechanisms that contribute to LOS deficiency and the resulting multidrug resistance phenotype are not understood. The overall objective of this proposal is to characterize and understand a novel multidrug resistance mechanism. The Specific Aims of this proposal are (i) to understand the genetic requirements for complete loss of LOS and (ii) to characterize the altered outer membrane permeability barrier in LOS deficient A. baumannii. Completion of this work will contribute a critical body of knowledge to the essentiality of LPS/LOS in Gram-negative bacteria and provide understanding of the molecular mechanisms required for a novel multidrug resistance mechanism. The basic science framework from this proposal could also potentially lead to development of novel therapeutics and improved vaccines.