2018年我国19株猪链球菌4型分离株的病原学特征及分析

Etiological characteristics and analysis of 19 isolates of Streptococcus suis serotype 4 in China, 2018

摘要:

[背景] 近年来，猪链球菌4型（Streptococcus suis serotype 4，SS4）分离率逐渐上升，但是有关SS4的系统研究报道匮乏。[目的] 研究19株SS4临床分离株的病原学特征。[方法] 以 2株猪链球菌2型（Streptococcus suis serotype 2，SS2）强毒株为参考菌株，对19株SS4分离株进行培养特性及形态学观察、生化试验、小鼠致病性试验、毒力基因检测、生物被膜形成能力测定和多位点序列分型。[结果] 19株SS4的菌落直径均较2株SS2大，溶血特性和镜检形态与SS2相同；多数SS4菌株（68.4%，13/19）与2株SS2的生化反应结果完全相同，少数菌株（31.6%，6/19）对乳糖、棉子糖、菊糖、蕈糖的发酵结果不完全相同；均可致小鼠脑膜炎和死亡，毒力最强的7株SS4与 2株SS2的LD₅₀同处于10⁷-10⁸ CFU/只数量级；均携带2-6种毒力基因，有5种毒力基因型，毒力基因型epf+mrp+sly+gapdh+fbps+orf2+占比最高（36.8%，7/19）；均具有生物被膜形成能力，以成膜力弱（1+）为主（89.5%，17/19），在扫描电镜下可见网状膜结构；有3种ST型，优势ST型为ST94 （89.5%，17/19），新发现2种ST型（ST1158和ST1224）。[结论] 19株SS4分离株的培养及形态学特性均一，生化特性多样，毒力基因型和ST型组成复杂，普遍具有生物被膜形成能力，对小鼠具有强致病性。

Abstract:

[Background] In recent years, the clinical isolation rate of Streptococcus suis serotype 4 (SS4) increased gradually, but systematic studies on SS4 were scarce.[Objective] In this research, we aimed to study on etiological characteristics of 19 isolates of SS4 in China, 2018. [Methods] 2 strains of Streptococcus suis serotype 2 (SS2) used as reference, 19 strains of SS4 were researched by cultural characteristics and morphological observation, biochemical test, animal pathogenicity test, virulence gene detection, determination of biofilm formation ability and multilocus sequence typing. [Results] Compared with 2 strains of SS2, 19 strains of SS4 had a larger colony diameter, the same hemolytic characteristics and microscopy morphology and incompletely same reaction to lactose, raffinose, synanthrin and mushroom sugar. All the strains of SS4 could caused meningitis and death in mice, and the LD₅₀ of the 7 most virulent strains of SS4 and 2 strains of SS2 were in the order of 10⁷-10⁸CFU. There were 2 to 6 virulence genes and 5 virulence genotypes in SS4, and epf+mrp+sly+gapdh+fbps+orf2+ was the dominant (36.8%, 7/19). All the strains of SS4 had the ability of biofilm formation, weak (1+) mainly (89.5%, 17/19), and the reticular biofilm structure was observed under scanning electron microscope. There were 3 ST types in SS4, of which ST94 were prevalent (89.5%, 17/19), while ST1158 and ST1224 were new found.[Conclusion] The culture and morphological characteristics of 19 strains of SS4 were uniform, the biochemical characteristics diverse, the virulence genotypes diverse, the biofilm formation ability generally owned, with strong pathogenicity to mice and genetic diversity.