DNA核酸酶与猪链球菌9型毒力的关系

摘要

[目的]除了猪链球菌2型外,猪链球菌9型(SS9)也是目前流行血清型,同时也是人畜共患病原菌.前期研究发现,DNA核酸酶(SsnA)存在于SS9毒力株中,在SS9无毒株中不存在.为明确SsnA对SS9毒力的影响,本研究构建ssnA缺失株ΔssnA,并研究其生物学功能.[方法]用穿梭质粒pSET-4s构建ΔssnA,并通过斑马鱼毒力试验、HEp-2细胞黏附、猪全血存活和酶活检测等试验,评价SsnA对SS9毒力的影响.[结果]斑马鱼毒力试验显示,ΔssnA对斑马鱼毒力显著降低,半数致死量是野生株的11.2倍;ΔssnA对HEp-2细胞的黏附率为野生株的60.61％;ΔssnA在猪全血中的存活率为野生株的71.88％;酶活试验表明,SsnA可降解线性和环状DNA.[结论]本研究表明SS9 SsnA具有降解线性和环状DNA能力,该基因缺失后细菌对斑马鱼毒力、黏附HEp-2细胞能力、在猪全血中存活及分解DNA能力都显著降低,证实SsnA是SS9的一个毒力因子.%[Objective] In addition to Streptococcus suis serotype 2,Streptococcus suis serotype 9 (SS9) is also a currently prevalent serotype and a zoonotic pathogen.In our previous study,SS9 DNA nuclease (SsnA) was considered as a candidate virulence factor.To clarify the impact of SsnA on SS9 virulence,we constructed ssnA mutant (ΔssnA) and studied its biological functions.[Methods] We evaluated the virulence of wild type strain and ΔssnA in a zebrafish infection model and compared the adherence rate to HEp-2 cells,the survival rate in pig blood,and enzymatic activity between wild type stain and ΔssnA.[Results] In a zebrafish infection experiment,the 50％ lethal dose value of ΔssnA was 11.2-fold higher than that of wild type strain.The adherence rate of ΔssnA to HEp-2 cells was only 60.61％ of the wild strain level.The survival rate of ΔssnA in pig blood was declined to 71.88％ of wild strain level.The enzymatic activity assay showed that SsnA can degrade both linear and circular DNA.[Conclusion] SsnA contributes to SS9 virulence in a zebrafish infection model,the adherence to HEp-2 cells,and the survival in pig blood.SsnA is indeed an essential virulence factor for SS9.