金黄色葡萄球菌CapB2在致病中的作用及表达调控机制研究

Staphylococcus aureus can causing a variety of illnesses ranging from benign, superficial skin eruptions to life-threatening infections.Capsular polysaccharides(CP) is a important virulence for S. aureus. Recently, capB2 located on the locus outside cap operon was found to be associated with the synthesis of CP. However, the role of capB2 in the pathogenicity of S. aueus is unclear. In our previous study, capB2 has been knocked out in S. aureus 75, named SA75 ΔcapB2 . The abscess size in mice caused by SA75 ΔcapB2 was significantly smaller than that by SA75 wild-type. The cell wall components of SA75 ΔcapB2 were significantly thinner than SA75 observed by Electron microscopy. These results indicated that the role of CapB2 in the synthesis of CP and pathogenicity of S. aureus was important. The present study will construct complementary strain of SA75 ΔcapB2 with plasmid containing capB2 and further investigate the role of CapB2 in the formation of abscess, synthesis of CP, colonization and immune evasion of S. aureus. Based on negative regulatory role of SarA in the expression of capB2 confirmed by our previous study, we will further investigate wether capB2 expression is directly regulated or indirectly via ArlRS、KdpDE and RbsR by SarA. The findings of the present study will help for finding CapB2 as a important potential target of drugs or vaccines for treating S.aureus infections.

金黄色葡萄球菌可引起从浅表的皮肤感染到威胁生命的严重感染。荚膜多糖是金黄色葡萄球菌重要的致病因子，近年来发现一个位于cap操纵子外的与荚膜多糖合成相关的基因（capB2），但其作用及表达调控机制不清楚。我们前期利用同源重组技术敲除了金黄色葡萄球菌75（SA75）的capB2，与SA75野生株相比，capB2敲除株感染小鼠后的脓肿面积显著减小，电镜观察发现细胞壁及相关成分明显变薄。我们推测CapB2在金黄色葡萄球菌荚膜形成和致病中发挥重要作用。本项目拟通过构建capB2缺失回复突变株，研究CapB2在金黄色葡萄球菌脓肿形成、荚膜形成、定植能力和免疫逃避等中的作用；在前期研究发现SarA对capB2具有负调控作用的基础上，进一步研究SarA是直接调控capB2表达还是通过ArlRS、KdpDE和 RbsR间接调控capB2表达。可以为开发抑制金黄色葡萄球菌关键毒力因子的药物或疫苗提供靶标。

金黄色葡萄球菌引起从浅表的皮肤感染到威胁生命的严重感染。细胞外荚膜多糖是金黄色葡萄球菌重要的致病因子之一。近年来发现一个位于cap操纵子外的与荚膜多糖合成相关的基因（capB2），但其作用及表达调控机制不清楚。.首先构建金黄色葡萄球菌capB2基因缺失回复株，通过小鼠皮肤脓肿模型，capB2基因阴性突变株感染的小鼠脓肿面积比野生株和回复株的脓肿面积小，提示capB2基因在皮肤感染形成的脓肿发挥重要作用，是重要的致病因子之一。观察capB2基因阴性突变株的微荚膜多糖比野生株和回复株的薄，提示capB2基因在微荚膜形成过程中发挥作用。capB2基因阴性突变株比野生株和回复株在全血中的存活率低，比与野生株和回复株共同作用的细胞释放的LDH少，提示CapB2在金黄色葡萄球菌感染中有一定的免疫逃逸作用。总之，我们证实CapB2在金黄色葡萄球菌荚膜形成和致病发挥重要作用。.通过荧光定量RT-PCR和EMSA研究SarA对capB的调控作用，结果发现金黄色葡萄球菌SarA对CapB2表达具有负调控作用并非通过SarA蛋白与cap2基因启动区序列直接结合直接发挥调控作用，而是通过间接调控的机制发挥作用。agr对cap2基因的表达是正调控作用。.我们研究了金黄色葡萄球菌SA75的capB2基因的上下游结构基因（capA2和capC2），通过构建两个基因的缺失突变株和回复株，以及三个基因之间的组合的基因突变株，证实金黄色葡萄球菌CapA2和CapC2的在致病性中的作用以及对荚膜多糖的形成作用小于CapB2。金黄色葡萄球菌SarA对CapA2和CapC2表达的负调控作用。

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