猪链球菌2型对扁桃腺上皮细胞的黏附和侵袭作用

猪链球菌2型(SS2)是重要的人畜共患病病原体，溶菌酶释放蛋白（MRP）是SS2的主要毒力因子之一。用天然表达MRP的江苏分离株HA9801和不表达MRP的上海分离株SH006444，研究SS2对仔兔扁桃腺上皮细胞的黏附和侵袭作用。黏附计数结果表明,HA9801（MRP+）和SH006444（MRP-）均能对扁桃腺上皮细胞高水平黏附。扫描和透射电镜均观察到HA9801的高水平黏附现象，黏附部位是细胞膜和细胞微绒毛，并观察到细胞膜上有链球菌正处于内化过程中。裂解记数结果表明，HA9801有低度侵袭力，SH006444未检测到侵袭力。结果提示，扁桃腺是SS2的定殖器官和感染门户；MRP＋菌株黏附后直接侵入细胞内是其穿过扁桃腺上皮细胞屏障的机制之一。

Adhesion and Invasion of Streptococcus suis Type 2 to Tonsil Epithelial Cells from Neonatal Rabbit

Streptococcus suis type 2 (SS2) is one of the most important zoonotic pathogens world wide. Muramidase released protein (MRP) is a key virulence factor of SS2. In this paper, both SS2 strains, HA9801, naturally with MRP expression, isolated from Jiangsu province and SH006444, without MRP, from Shanghai, were used to study adhesion and invasion of SS2 to tonsil epithelial cells from neonatal rabbit. Adhesion counting assay demonstrated high adhesive levels of both strains. Scanning and transmission electron microscope observation further showed a dense adhering of HA9801 at cellular membrane and microvilli, and HA9801 cells were being internalized by the cell membrane. Lysis counting assay revealed a weak invasion of HA9801 and no invasion of SH006444 to tonsil epithelial cells from neonatal rabbit. Findings of this study suggested, firstly, the tonsil served as the colonizing site and an entrance of SS2 in establishment of infection; secondly, the direct invasion into epithelial cells following their adhesion was one of their mechanisms of breaking through the tonsil epithelial cell barrier.