背景:亲水性,革兰氏阳性致病链球菌肺炎的脂磷壁酸(LTA)的聚合链通过脂磷壁酸连接酶TacL共价连接到糖基甘油脂-D-吡喃葡萄糖基-(1,3)-二酰甘油,导致其固定在细胞质膜中。肺炎球菌LTA,与壁磷壁酸共享相同的重复单元,对于正常生长是可有可无的,但对于侵袭性感染的全毒力是必需的。
方法:对构建的TacL缺陷和互补菌株的突变体进行生长测试,抗氧化应激和抗菌肽的敏感性。Further,肺炎球菌的膜流动性,评估了它们在Galleriamelonella以及鼻内小鼠感染模型中粘附于肺上皮细胞的能力和毒力。
结果:在本研究中,我们表明,在小鼠鼻内感染模型中,LTA对于肺炎球菌粘附人鼻咽细胞和定植已经是不可或缺的.缺乏TacL的突变体未显示形态缺陷。然而,我们对不同血清型肺炎球菌膜的分析显示,在缺乏LTA而非WTA的突变体中,脂蛋白的膜流动性和表面蛋白丰度改变.这些突变体的膜流动性下降,表现出更多的脂蛋白,并显示对抗菌肽的敏感性增加。在互补的突变菌株中,这种缺陷已完全恢复。
结论:综合来看,LTA对于定殖至关重要,并且需要通过维持膜完整性来有效保护肺炎球菌免受先天免疫防御机制的影响。
BACKGROUND: The hydrophilic, polymeric chain of the lipoteichoic acid (LTA) of the Gram-positive pathobiont Streptococcus pneumoniae is covalently linked to the glycosylglycerolipid α-
d-glucopyranosyl-(1,3)-diacylglycerol by the LTA ligase TacL, leading to its fixation in the cytoplasmic membrane. Pneumococcal LTA, sharing identical repeating units with the wall teichoic acids (WTA), is dispensable for normal growth but required for full virulence in invasive infections.
METHODS: Mutants deficient in TacL and complemented strains constructed were tested for their growth, resistance against oxidative stress, and susceptibility against antimicrobial peptides. Further, the membrane fluidity of pneumococci, their capability to adhere to lung epithelial cells, and virulence in a Galleria mellonella as well as intranasal mouse infection model were assessed.
RESULTS: In the present study, we indicate that LTA is already indispensable for pneumococcal adherence to human nasopharyngeal cells and colonization in an intranasal mouse infection model. Mutants deficient for TacL did not show morphological defects. However, our analysis of pneumococcal membranes in different serotypes showed an altered membrane fluidity and surface protein abundance of lipoproteins in mutants deficient for LTA but not WTA. These mutants had a decreased membrane fluidity, exhibited higher amounts of lipoproteins, and showed an increased susceptibility to antimicrobial peptides. In complemented mutant strains, this defect was fully restored.
CONCLUSIONS: Taken together, LTA is crucial for colonization and required to effectively protect pneumococci from innate immune defence mechanisms by maintaining the membrane integrity.