Department of Molecular Microbiology and Biotechnology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.
Porter School for the Environment, Tel Aviv University, Tel Aviv, Israel.
mBio. 2018 Jul 3;9(4):e01070-18. doi: 10.1128/mBio.01070-18.
Many strains of carry a 29,250-bp ETT2 pathogenicity island (PAI), which includes genes predicted to encode type III secretion system (T3SS) components. Because it is similar to the pathogenicity island 1 (SPI-1) system, encoding a T3SS in , it was assumed that ETT2 also encodes a secretion system injecting effectors into host cells. This assumption was checked in serotype O2-associated with urinary tract infections and septicemia-which has an intact ETT2 gene cluster, in contrast to most strains in which this cluster carries deletions and mutations. A proteomic search did not reveal any putative secreted effector. Instead, the majority of the secreted proteins were identified as flagellar proteins. A deletion of the ETT2 gene cluster significantly reduced the secretion of flagellar proteins, resulting in reduced motility. There was also a significant reduction in the transcriptional level of flagellar genes, indicating that ETT2 affects the synthesis, rather than secretion, of flagellar proteins. The ETT2 deletion also resulted in additional major changes in secretion of fimbrial proteins and cell surface proteins, resulting in relative resistance to detergents and hydrophobic antibiotics (novobiocin), secretion of large amounts of outer membrane vesicles (OMVs), and altered multicellular behavior. Most important, the ETT2 deletion mutants were sensitive to serum. These major changes indicate that the ETT2 gene cluster has a global effect on cell surface and physiology, which is especially important for pathogenicity, as it contributes to the ability of the bacteria to survive serum and cause sepsis. Drug-resistant extraintestinal pathogenic (ExPEC) strains are major pathogens, especially in hospital- and community-acquired infections. They are the major cause of urinary tract infections and are often involved in septicemia with high mortality. ExPEC strains are characterized by broad-spectrum antibiotic resistance, and development of a vaccine is not trivial because the ExPEC strains include a large number of serotypes. It is therefore important to understand the virulence factors that are involved in pathogenicity of ExPEC and identify new targets for development of antibacterial drugs or vaccines. Such a target could be ETT2, a unique type III secretion system present (complete or in parts) in many ExPEC strains. Here, we show that this system has a major effect on the bacterial surface-it affects sensitivity to drugs, motility, and secretion of extracellular proteins and outer membrane vesicles. Most importantly, this system is important for serum resistance, a prerequisite for septicemia.
许多 菌株携带一个 29250bp 的 ETT2 致病性岛（PAI），其中包括预测编码 III 型分泌系统（T3SS）组件的基因。因为它类似于 致病岛 1（SPI-1）系统，编码 中的 T3SS，因此假设 ETT2 也编码一个将效应物注入宿主细胞的分泌系统。这一假设在与尿路感染和败血症相关的血清型 O2 中得到了验证，该血清型 O2 具有完整的 ETT2 基因簇，而大多数菌株的该基因簇缺失和突变。蛋白质组搜索未发现任何推定的分泌效应物。相反，大多数分泌蛋白被鉴定为鞭毛蛋白。ETT2 基因簇的缺失显著减少了鞭毛蛋白的分泌，导致运动性降低。鞭毛基因的转录水平也显著降低，表明 ETT2 影响鞭毛蛋白的合成，而不是分泌。ETT2 缺失还导致菌毛蛋白和细胞表面蛋白分泌的其他重大变化，导致对去污剂和疏水性抗生素（新生霉素）的相对抗性、大量外膜囊泡（OMV）的分泌以及多细胞行为的改变。最重要的是，ETT2 缺失突变体对血清敏感。这些重大变化表明，ETT2 基因簇对细胞表面和生理学具有全局影响，这对致病性尤为重要，因为它有助于细菌在血清中存活并引起败血症的能力。耐药性肠外致病性 （ExPEC） 菌株是主要病原体，尤其是在医院和社区获得性感染中。它们是尿路感染的主要原因，常与高死亡率的败血症有关。ExPEC 菌株的特点是广谱抗生素耐药性，由于 ExPEC 菌株包括大量血清型，因此开发疫苗并非易事。因此，了解参与 ExPEC 致病性的毒力因子并确定用于开发抗菌药物或疫苗的新靶点非常重要。这样的靶点可以是 ETT2，它是许多 ExPEC 菌株中存在的（完整或部分）独特的 III 型分泌系统。在这里，我们表明该系统对细菌表面有重大影响——它影响药物敏感性、运动性以及细胞外蛋白和外膜囊泡的分泌。最重要的是，该系统对血清抗性很重要，这是败血症的先决条件。
