College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
Microb Pathog. 2010 Mar-Apr;48(3-4):103-9. doi: 10.1016/j.micpath.2009.11.005. Epub 2009 Nov 26.
Streptococcus suis is an important swine and human pathogen, and also an emerging zoonotic agent. A surface-associated subtilisin-like serine protease (SspA) of S. suis was identified by screening a genomic expression library as fragments of this protein reacted most strongly with convalescent-phase pig sera. The sspA gene is present in 29 of 33 S. suis serotypes reference strains and is expressed on the surface of S. suis. Relative real-time quantitative PCR assay demonstrated that sspA mRNA expression in vivo was several thousand fold of that in vitro. A sspA(-) mutant was generated from a S. suis serotype 2 strain SC19 by allelic exchange. The mutant was not different from the wild type strain in subcellular structures and in hemolytic phenotype. However, the virulence of the sspA(-) mutant was markedly lower than the wild type in pigs as demonstrated in experimental infections. These data indicated that the surface-associated protein SspA is a conserved virulence factor of S. suis and is involved in the pathogenesis of S. suis.
猪链球菌是一种重要的猪和人类病原体，也是一种新兴的人畜共患病原体。通过筛选基因组表达文库，我们鉴定出一种与恢复期猪血清反应最强的表面相关的枯草杆菌蛋白酶样丝氨酸蛋白酶（SspA）。sspA 基因存在于 33 种猪链球菌血清型参考菌株中的 29 种中，并且在猪链球菌的表面表达。相对实时定量 PCR 检测表明，sspA 在体内的 mRNA 表达是体外的数千倍。通过基因同源重组，我们从猪链球菌血清型 2 菌株 SC19 中构建了 sspA 缺失突变株。该突变株与野生型菌株在亚细胞结构和溶血表型上没有差异。然而，在猪的实验感染中，sspA 缺失突变株的毒力明显低于野生型菌株。这些数据表明，表面相关蛋白 SspA 是猪链球菌的一种保守毒力因子，参与了猪链球菌的发病机制。
