应用比较转录谱鉴定猪链球菌新的致病基因及致病基因的功能研究

Streptococcus suis is a major swine pathogen. Moreover, it is also an emerging zoonotic agent. In 2005, one big outbreak of S. suis in humans appeared in China with serious cases of streptococcal toxic shock-like syndrome (STSLS). The strain responsible for the outbreak was originally characterized in our laboratory by multilocus sequence typing (MLST) as sequence type (ST) 7. In our previous study, We found that the ST7 epidemic strain possessed the capacity to induce significantly higher levels of pro-inflammatory cytokines and chemokines than ST1 strains and ST25 strains in vitro and in vivo. The excessive pro-inflammatory cytokines and chemokines induced by ST7 strains were also proved to be responsible for the STSLS. However, there are so far no clear explanations which components contribute to the property of ST7 strains. A population structure analysis by using minimum core genome (MCG) classified S.suis isolates into seven MCG groups, of which pathogenic differences among MCG groups were found. Evaluating the public health significance of different MCG groups will facilitates the surveillance of S. suis with the potential to cause severe clinical infections and large-scale outbreaks. The analysis of known putative virulence genes among the MCG groups can not explain the pathogenic differences among MCG groups. More potential virulence genes are needed to include...The proposal prepare to identify novel pathogenic genes of S.suis by comparing the expression profiles among ST1, ST7 and ST25 strains. The function of these genes will be investigated. The study will reveal mechanisms and components of S. suis ST7 epidemic strain to induce excessive inflammation responsible for the high prevalence of STSLS. The proposal will also provide new traget genes to evaluate the pathogenic differences among MCG groups.

猪链球菌是一种重要的人兽共患病病原。2005年序列7（ST7）型猪链球菌在中国引起大的人间疫情，有患者出现链球菌中毒性休克样综合症。我们研究发现，和国外代表性菌株ST25、ST1相比，ST7型菌株毒力增强，可刺激宿主产生细胞因子风暴，导致休克和死亡。ST7型菌株刺激机体产生过量细胞因子的机制研究已取得很大进展，但相关细菌组分依然未能在ST7型菌株基因组中准确定位。使用最小核心基因组（MCG）分型技术将猪链球菌种群分为7个MCG组，精确鉴定不同MCG组的致病力水平，有助于快速评估感染风险，制定有针对性的预防控制措施。仅分析现有毒力基因已不能满足这种致病力比较研究，需要引入新的分析思路。本课题拟通过比较不同致病能力猪链球菌感染宿主后的基因转录谱差异，发现猪链球菌新的致病相关基因并开展功能研究，一方面阐明ST7型猪链球菌致病力增强的机理，同时为MCG组间致病菌致病致病能力比较研究提供技术支撑。

猪链球菌是一种重要的人兽共患病病原菌，相同血清型菌株间的致病力差异极大，致病力与序列型（ST）密切相关。ST7型猪链球菌只在中国流行，致病力增强并引起1998年江苏和2005年四川两次疫情。ST7型菌株致病力增强的机理依然未明确。本研究通过比较不同致病能力的ST7, ST1与ST25型猪链球菌感染宿主后的转录谱差异，发现了ST7型菌株有14个基因在与宿主细胞相互作用早期的表达量特异升高。通过构建相关基因的缺失株与野生株进行斑马鱼致病力比对研究，结果显示9个基因缺失株的斑马鱼生存率显著高于野生株SC84，表明这9个基因与ST7型菌株致病力增强密切相关。体外细胞因子结果表明10个基因缺失后刺激BV2细胞分泌IL-6与TNF-α能力显著下降，3个基因仅参与刺激BV2细胞分泌IL-6的途径。这一结果为进一步阐明ST7型猪链球菌致病力增强的机理提供了新的思路；本研究还确定了ST1型菌株的12个基因在与宿主细胞相互作用晚期特异表达升高，表明ST7与ST1的致病机理有差异；本研究初步确定了176个基因在ST7与ST1型菌株中表达增高，将其定义为猪链球菌新的致病相关基因。生物信息分析表明这些基因在不同致病力菌株间存在明显的序列变异，该结果为猪链球菌种群的不同基因型、血清型菌株的致病能力评估提供了技术支撑。