IncFII质粒是介导耐药基因在肠杆菌科细菌中传播的主要载体之一，IS26转座子的复制重组常与耐药基因在质粒间的转移有关，本课题组在预实验中发现，野生型质粒Pst-41NDM在新宿主菌内进化过程中，IS26携带的部分耐药基因有缺失，质粒的适应性代价也有所降低。因此，我们推测IS26复制重组也可能与IncFII质粒在宿主菌内适应性的调节有关。本研究将筛选临床分离携带IS26转座子的IncFII耐药质粒的肠杆菌科细菌，用二代测序方法分析菌株的种系相关性、相似质粒进化和质粒的融合情况；检测Pst-41NDM质粒在不同ST型菌株中的进化和稳定性；针对IS26突变株EC958/Pst-41NDM(evo)，用GWAS分析和转录组学分析，筛选和验证主导全局性调控系统基因的关键突变点，最终明确IS26重组介导质粒适应性代价的调节及调控机制，为寻找IncFII质粒与宿主适应性的关键因素提供理论依据。

The IncFII plasmid is one of the main vector for the transmission of many antibiotic resistant genes in Enterobacteriaceae. The replicative recombination of IS26 transposon is often associated with the transfer of antibiotic resistant genes between different plasmids. In our preliminary experiment, we found that, during the evolution of wild-type plasmid pst-41NDM in the new host bacteria, some of the antibiotic resistance genes carried by IS26 was deleted, and the plasmid fitness costs was also reduced. Therefore, we hypothesized that IS26 replicative recombination may be related to the regulation of IncFII plasmid fitness cost in the host. In this study, the clinically isolated Enterobacteriaceae carrying IncFII plasmid with IS26 transposon will be screened , and the phylogenetic correlation of strains, the evolutionary relationship between similar plasmids, the fusion situation of the plasmids will be analyzed by second-generation sequencing. The evolution and stability of Pst-41NDM plasmid in different ST types of Enterobacteriaceae will be detected. The key mutation points of genes that dominate the global regulatory system in the IS26 mutant strain EC958/Pst-41NDM(evo) will be screened and verified by Genome-wide association study and transcriptome analysis. Finally, the regulatory process and related regulatory mechanism of plasmid fitness cost mediated by IS26 transposon site-specific recombination will be determined. This study will provide theoretical basis for the determination of the key factors for IncFII plasmid-host adaptation.