中文摘要：

目的 研究新的细胞壁锚定蛋白SasX对金黄葡萄球菌生物膜形成及毒力的影响.方法 采用基因敲除及基因互补技术获得耐甲氧西林金黄葡萄球菌（MRSA） ST-239 HS770 sasX基因突变株及基因互补株,应用半定量生物膜形成试验检测sasX基因突变前后对金黄葡萄球菌生物膜形成的影响,使用小鼠皮肤脓肿形成模型研究SasX对金黄葡萄球菌毒力的影响.结果 采用pKOR1质粒构建重组质粒并成功获得sasX基因敲除株.与野生株相比,突变株HS770△sasX生物膜形成能力明显减弱（P＜0.05）,互补表达株HS770△sasX（pRBsasX）生物膜形成能力无明显统计学差异（P＞0.05）.与野生株相比,突变株HS770△sasX初始黏附能力明显减弱（P＜0.05）,互补表达株HS770△sasX（pRBsasX）初始黏附能力无明显统计学差异（P＞0.05）.HS770和HS770△sasX接种小鼠后均形成明显的脓肿,PBS对照组小鼠皮肤表面未见脓肿产生.细菌接种后第2天小鼠皮肤脓肿面积达到最大,随着接种时间的延长小鼠皮肤脓肿面积逐渐缩小.但是从接种后第1天开始,HS770接种组小鼠皮肤脓肿形成面积在同一时间点上明显大于HS770△sasX接种组（P＜0.05）.结论 采用pKOR1质粒进行基因敲除可以明显提高目的基因的敲除效率.SasX可以通过影响细菌的初始黏附从而影响生物膜的形成,SasX是金黄葡萄球菌在医院环境内持续感染重要的毒力因子.

英文摘要：

Objective To determine whether the novel surface-anchored protein SasX mediates biofilm formation of Staphylococcus aureus and to investigate the function of SasX in the virulence of S.aureus.Methods Methicillin-resistant Staphylococcus aureus（MRSA） ST-239 HS sasX gene mutant （HS770 △ sasX） and complement [ HS770 △sasX（pRBsasX） ] were gotten by gene knock out and complement methods.Semiquantitative biofilm assay was used for detection of the biofilm formation of wild type and mutant.By using abscess model in mice,we investigate the function of SasX in the virulence of S.aureus.Results The sasX gene mutant strain was gotten successfully by using pKOR1 plasmid.HS770 △sasX with a very clear reduction of biofilm formation compared to wild type and complement（P〈0.05）,there was no significant difference of biofilm formation between wild type and complement（P〉0.05）.Primary attachment assays demonstrated that comparing to wild type,there was significant reduction of initial accumulative phases of biofilm development in HS770△sasX（P〈0.05）,but there was no difference between wild type and complement（P〉0.05）.Both sasX wild type and mutant could cause abscess in the skin of mice,no abscess were forming in the PBS control group.The biggest abscess size was found on the second day after injection.The size of abscess was smaller with extension of the time.But on the same time,the wild type group produced significantly larger abscesses compared to mutant group（ P〈0.05 ）.Conclusion It could improve the effect of gene knocking out by using pKOR1 plasmid.SasX promotes biofilm formation by influencing on the initial accumulative phases of biofilm development,SasX is a marker of invasive infection of S.aureus,it is very important for S.aureus persistence in the hospital setting.