Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom.
PLoS One. 2012;7(8):e43046. doi: 10.1371/journal.pone.0043046. Epub 2012 Aug 15.
Staphylococcus aureus is a leading cause of bacteraemia, which frequently results in complications such as infective endocarditis, osteomyelitis and exit from the bloodstream to cause metastatic abscesses. Interaction with endothelial cells is critical to these complications and several bacterial proteins have been shown to be involved. The S. aureus extracellular adhesion protein (Eap) has many functions, it binds several host glyco-proteins and has both pro- and anti-inflammatory activity. Unfortunately its role in vivo has not been robustly tested to date, due to difficulties in complementing its activity in mutant strains. We previously found Eap to have pro-inflammatory activity, and here show that purified native Eap triggered TNFα release in whole human blood in a dose-dependent manner. This level of TNFα increased adhesion of S. aureus to endothelial cells 4-fold via a mechanism involving protein A on the bacterial surface and gC1qR/p33 on the endothelial cell surface. The contribution this and other Eap activities play in disease severity during bacteraemia was tested by constructing an isogenic set of strains in which the eap gene was inactivated and complemented by inserting an intact copy elsewhere on the bacterial chromosome. Using a murine bacteraemia model we found that Eap expressing strains cause a more severe infection, demonstrating its role in invasive disease.
金黄色葡萄球菌是导致菌血症的主要原因之一，常导致感染性心内膜炎、骨髓炎和从血液中流出引起转移性脓肿等并发症。与内皮细胞的相互作用对这些并发症至关重要，已经证明几种细菌蛋白参与其中。金黄色葡萄球菌细胞外黏附蛋白（Eap）具有多种功能，它结合几种宿主糖蛋白，具有促炎和抗炎活性。不幸的是，由于在突变株中补充其活性的困难，其在体内的作用迄今尚未得到充分验证。我们之前发现 Eap 具有促炎活性，并且这里显示纯化的天然 Eap 以剂量依赖的方式在全人血中触发 TNFα 释放。这种 TNFα 水平通过细菌表面的蛋白 A 和内皮细胞表面的 gC1qR/p33 增加了 S. aureus 与内皮细胞的黏附 4 倍。通过构建一组基因缺失和在细菌染色体的其他位置插入完整拷贝来互补的基因同源菌株，测试了这种 Eap 及其它 Eap 活性在菌血症期间疾病严重程度中的作用。使用鼠菌血症模型，我们发现表达 Eap 的菌株导致更严重的感染，证明了它在侵袭性疾病中的作用。
