中文摘要：

目的构建猪链球菌2型（Streptococcus suis serotype2，S．suis2）中国强致病株05ZYH33荚膜缺陷株。方法利用同源重组基因敲除方法获得S．suis2强毒株05ZYH33荚膜合成基因cps2B敲除突变株，通过小鼠攻毒实验证实荚膜缺陷株对细菌毒力的影响。结果PCR和Southern杂交结果均显示cps2B基因完全被壮观霉素抗性基因替代，表明基因敲除突变体构建成功。电镜结果证实突变体荚膜合成能力缺失，小鼠致病性实验结果显示突变体毒力基本丧失。结论成功构建05ZYH33荚膜缺陷株，提示菌体荚膜多糖成分对于猪链球菌2型侵袭和致病具有显著作用。

英文摘要：

Objective To construct a mutant of Streptococcus suis serotype 2 （S. suis 2） virulent strain 05ZYH33 by knocking out its cps2B gene which encoding capsular polysaccharide （CPS） synthase. Methods The cps2B gene in this 05ZYH33 strain was knocked out based on the principle of homologous recombination. PCR analysis and Southern hybridization were used to identify the knockout. Transmission electron microscopy was employed to observe the morphology of the established strain. The virulence of the deficient strain was tested on the murine model of infection. Results PCR analysis and Southern hybridization showed that cps2B was replaced completely by the Spc cassette （encoding the gene resistant to spectinomycin）. No capsular material was observed on the surfaces of the mutant strain by transmission electron microscopy, suggesting that S. suis 2 mutant loss of ability in capsule synthesis. Furthermore, the nonencapsulated mutant was completely avirulent in murine model of infection. Conclusion The cps2B gene deletion mutant of 05ZYH33 was successfully constructed. The CPS synthase of S. suis 2 plays an essential role in the pathogenesis and invasiveness of S. suis 2 infection.