PDF(Pubmed)
Abstract：
Acinetobacter baumannii is a Gram-negative bacterial pathogen that poses a major health concern due to increasing multidrug resistance. The Gram-negative cell envelope is a key barrier to antimicrobial entry and includes an inner and outer membrane. The maintenance of lipid asymmetry (Mla) system is the main homeostatic mechanism by which Gram-negative bacteria maintain outer membrane asymmetry. Loss of the Mla system in A. baumannii results in attenuated virulence and increased susceptibility to membrane stressors and some antibiotics. We recently reported two strain variants of the A. baumannii type strain ATCC 17978: 17978VU and 17978UN. Here, ∆mlaF mutants in the two ATCC 17978 strains display different phenotypes for membrane stress resistance, antibiotic resistance, and pathogenicity in a murine pneumonia model. Although allele differences in obgE were previously reported to synergize with ∆mlaF to affect growth and stringent response, obgE alleles do not affect membrane stress resistance. Instead, a single-nucleotide polymorphism (SNP) in the essential gene encoding undecaprenyl pyrophosphate (Und-PP) synthase, uppS, results in decreased enzymatic rate and decrease in total Und-P levels in 17978UN compared to 17978VU. The UppSUN variant synergizes with ∆mlaF to reduce capsule and lipooligosaccharide (LOS) levels, increase susceptibility to membrane stress and antibiotics, and reduce persistence in a mouse lung infection. Und-P is a lipid glycan carrier required for the biosynthesis of A. baumannii capsule, cell wall, and glycoproteins. These findings uncover synergy between Und-P and the Mla system in maintaining the A. baumannii cell envelope and antibiotic resistance.IMPORTANCEAcinetobacter baumannii is a critical threat to global public health due to its multidrug resistance and persistence in hospital settings. Therefore, novel therapeutic approaches are urgently needed. We report that a defective undecaprenyl pyrophosphate synthase (UppS) paired with a perturbed Mla system leads to synthetically sick cells that are more susceptible to clinically relevant antibiotics and show reduced virulence in a lung infection model. These results suggest that targeting UppS or undecaprenyl species and the Mla system may resensitize A. baumannii to antibiotics in combination therapies. This work uncovers a previously unknown synergistic relationship in cellular envelope homeostasis that could be leveraged for use in combination therapy against A. baumannii.
摘要：
鲍曼不动杆菌是一种革兰氏阴性细菌病原体，由于多药耐药性的增加而引起了主要的健康问题。革兰氏阴性细胞包膜是抗微生物剂进入的关键屏障,并且包括内膜和外膜。脂质不对称（Mla）系统的维持是革兰氏阴性细菌维持外膜不对称的主要稳态机制。鲍曼不动杆菌中Mla系统的丧失导致毒力减弱和对膜应激源和一些抗生素的敏感性增加。我们最近报道了鲍曼不动杆菌型菌株ATCC17978的两种菌株变体:17978VU和17978UN。这里,两个ATCC17978菌株中的ΔmlaF突变体显示出不同的膜胁迫抗性表型，抗生素耐药性,和致病性在鼠肺炎模型。尽管之前报道了bgE的等位基因差异与ΔmlaF协同作用以影响生长和严格反应，obgE等位基因不影响膜胁迫抗性。相反，单核苷酸多态性（SNP），在编码十一烯基焦磷酸盐（Und-PP）合酶的必需基因，uppS,与17978VU相比，17978UN的酶速率降低，总Und-P水平降低。UppSUN变体与ΔmlaF协同作用，以降低胶囊和脂寡糖（LOS）水平，增加对膜应力和抗生素的敏感性，并减少小鼠肺部感染的持久性。Und-P是鲍曼不动杆菌胶囊生物合成所需的脂质聚糖载体，细胞壁,和糖蛋白。这些发现揭示了Und-P和Mla系统在维持鲍曼不动杆菌细胞包膜和抗生素抗性方面的协同作用。鲍曼不动杆菌因其多重耐药性和在医院环境中的持久性而对全球公共卫生构成严重威胁。因此,迫切需要新的治疗方法。我们报告说，与扰动的Mla系统配对的有缺陷的十一烯基焦磷酸盐合酶（UppS）导致合成的患病细胞，这些细胞更容易受到临床相关抗生素的影响，并在肺部感染模型中显示出降低的毒力。这些结果表明，靶向UppS或十一戊烯属物种和Mla系统可能会使鲍曼不动杆菌在联合治疗中对抗生素重新敏感。这项工作揭示了细胞包膜稳态中先前未知的协同关系，可用于联合治疗鲍曼不动杆菌。
