DNA核酸酶与猪链球菌9型毒力的关系

Relationship between DNA nuclease and the virulence of Streptococcus suis serotype 9

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。

Abstract:

[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.