PSM-mec毒素介导表皮葡萄球菌逃逸机体中性粒细胞的吞噬和杀伤的作用机制

表皮葡萄球菌是定植在人体皮肤最常见的益生菌，也是医源性感染的重要机会致病菌。PSM家族是表皮葡萄球菌产生的唯一一类毒素，其中PSM-mec已逐步被证实在金黄色葡萄球菌致病过程中发挥重要作用。申请者在前期成功构建表皮葡萄球菌菌株RP62A和SE620的Δpsm-mec缺失突变和Δpsm-mec*启动子点突变的同源异构体，分别在动物模型、组织细胞水平证实了PSM-mec毒素在表皮葡萄球菌所致败血症发生过程中发挥关键作用。在败血症小鼠外周血和肾脏组织中及人外周血和中性粒细胞中，野生株的存活数量均显著高于Δpsm-mec突变株。由此推测，PSM-mec毒素可介导表皮葡萄球菌逃逸机体中性粒细胞的免疫防御。为证实这一假说，本研究拟从分子、细胞和动物水平论证PSM-mec毒素对中性粒细胞吞噬、氧依赖杀伤途径及胞外诱捕网的影响，为阐明表皮葡萄球菌感染的发病机制及临床治疗方案的制订提供新思路。

Staphylococcus epidermidis---the predominant commensal microorganism on the human skin is an important "accident" pathogen. The only one kind of toxin that staphylococcus epidermidis can produce is PSM. PSM-mec belongs to PSM family, which has been implicated connects virulence to methicillin resistance in MRSA. We produced isogenic psm-mec deletion mutants (Δpsm-mec) in two staphylococcus epidermidis strains, a clinical isolate strain SE620 and the genome-sequenced strain RP62A. We also introduced a point mutation in the start codon of the psm-mec gene in the genome of strain SE620 to differentiate between effects mediated by the PSM-mec peptide versus those due to the psm-mec srRNA (psm-mec*). By using tissue culture and animal infection model-based evidence, PSM-mec toxin produced by staphylococcus epidermidis has a strong impact on the severity of sepsis and its outcome. We showed that CFU of Δpsm-mec mutant strains in peripheral blood and kidney of sepsis mouse were significantly decreased in contrast to its parent strain. Moreover, there was a similar result in human blood and neutrophils. In order to explore the immune stragies escaping from neutrophils by staphylococcus epidermidis toxin, a set of experiments both in vivo and in vitro will be taken in this study. We will investigate staphylococcus epidermids resistants to phagocytosis, oxgen burst and NETs of nuetrophils induced by PSM-mec toxin. The potential molecular mechanism of staphylococcus epidermidis infection will be explored and the results may suggest new virulence-targeted therapeutic approaches in the future.