近5年，无乳链球菌病已严重影响我国罗非鱼产业可持续发展。项目组在2006-2013年我国罗非鱼链球菌病流行病学系统研究的基础上，结合国内外学者研究结果，提出"我国罗非鱼源无乳链球菌可能来源于人"的学术主张。为此，项目拟通过菌株临床信息、血清型及基因型比较研究，初步理清我国罗非鱼源与人源无乳链球菌间进化亲缘关系；同时，通过感染试验、4株罗非鱼源和人源菌株（能/不能感染罗非鱼）全基因组测序及比较分析，从基因组水平进一步阐明我国罗非鱼源与人源无乳链球菌的亲缘关系及人源无乳链球菌跨宿主感染罗非鱼的分子机制；另外，利用基因突变和缺失、转录组分析、RNAi及免疫组化等技术对毒力因子、转移元件及其它关键基因在人源无乳链球菌跨宿主感染罗非鱼脑膜细胞的作用机制进行研究。项目探讨中国罗非鱼源与人源无乳链球菌的亲缘关系及人源无乳链球菌跨宿主感染的分子机制，为科学防控无乳链球菌病提供实验和理论依据。

Streptococcus agalactiae has significantly impacted the sustainable development of tilapia industry around these five years in China. Depending on our previous system study on the epidemiology of streptococcal disease in Tilapia during a period of 2006 to 2013, making together with studies by domestic and foreign scholars, our research group has proposed an academic hypothesis that human-to-fish transmission of Streptococcus agalactiae. Based on the above consideration, this project is proposed to study the evolution and relationships between tilapia-derived and human-derived wild-type S.agalactiae speices through comparison analyses of their clinical experimental informations, serotypes and genotypes. Meanwhile, in order to explain evolution relationship between tilapia source and human source S.agalactiae and the molecular mechanism of Tilapaia infected S.agalactiae from human, sequencing and comparing four strains of different resources of wild-type S.agalactiae isolated from fish and human (include the stains can and not can infected Tilapia) whole genome DNA. In addition, functional mechanism of virulent facors, transfer elements, or some other active key genes in the processing of such pathogenic human-derived S.agalactiae to cross species barriers to infect tilapia meningeal cells, will be studied by gene mutation and deletion, transcriptome analysis, RNA interferene, and immunohistochemical technologies. In sum, this project aim to discusses the evolution and relationships between tilapia-derived and human-derived S.agalactiae speices in China, as well as the molecular mechanism of S.agalactiae cross-species host transmission, provide experimental and theoretical basis for scientific prevention and control of S.agalactiae disease.