近期肺炎克雷伯菌临床分离株呈现多重耐药与高毒力合并进化的趋势，使其成为最令人担忧的下一个超级细菌。细菌CRISPR/Cas系统具有抵御外源DNA入侵的能力，并且可通过靶向细菌自身基因实现内源性调控；但目前这一系统对肺炎克雷伯菌致病性的影响尚不明确。前期通过对肺炎克雷伯菌CRISPR/Cas系统的分析，我们发现高毒力菌株普遍携带CRISPR/Cas系统，并且其中的间隔序列能够靶向生物膜形成相关质粒以及菌株自身序列。我们推测CRISPR/Cas系统能通过作用于特定靶序列，对肺炎克雷伯菌的毒力和生物膜形成进行调控。因此，本项目基于课题组前期测序的二百多株肺炎克雷伯菌临床分离株将：（1）比较不同表型和基因型分离株携带CRISPR/Cas系统及其突变情况，（2）解析CRISPR特异性间隔序列对菌株表型和靶基因转录水平的影响，（3）揭示CRISPR/Cas系统调控毒力和生物膜形成的关键节点和调控网络。

Recently the trend of co-evolution of multi-drug resistance and high virulence of Klebsiella pneumoniae makes it become one of the most alarming next superbugs. Clustered regularly interspaced short palindromic repeats and their associated proteins (CRISPR/Cas) not only enable bacteria to have an immune defense against exogenous DNA invasion, but also can regulate endogenous genes by targeting bacterial genome. However, the effect of this system on the pathogenicity of Klebsiella pneumoniae remains unclear. According to previous studies and analysis on whole genome sequence data, we found that hypervirulent Klebsiella pneumoniae were more likely to carry CRISPR/Cas system. And the CRISPR/Cas system normally harbor spacers targeting chromosome sequences and plasmids involved with biofilm formation. Thus, we speculate that CRISPR/Cas system could regulate the virulence and biofilm formation of Klebsiella pneumoniae by targeting associated endogenous sequences. Therefore, on the basis of more than 200 Klebsiella pneumoniae isolates performed whole genome sequencing, this study aims to (1) compare the phenotypes and genotypes in isolates carrying distinct CRISPR/Cas system, (2) explore the effect of specific spacer sequence on phenotype and expression of target gene at transcription level, (3) and reveal the key nodes and regulatory networks that CRISPR/Cas system regulates virulence and biofilm formation.