Streptococcus agalactiae secrete virulence factors believed to be able of killing host tissues, especially under elevated water temperature. A direct effect of S. agalactiae secretory products on tilapia cells was tested on the tilapia kidney (TK‐1) cell culture. The bacteria were cultured under four different temperature levels: 22, 29, 32 and 37°C; the cell‐free portion was processed through SDS‐PAGE; and distinct bands were identified by LC‐MS/MS. At least, three virulence factors were identified, Bsp, PcsB and CAMP factor, with increasing levels as the cultured temperature rose. Expressions of bsp, pcsB and cfb were also up‐regulated with the rising of the temperature in S. agalactiae culture. The supernatant from the bacteria cultured under specified temperatures was added into TK‐1 cell‐cultured wells. Morphological damage and mortality of the cultured cells, as determined by MTT method, were increased progressively from the supernatant treatment according to the rise of temperature in S. agalactiae culture. This study suggests that the production of the three virulence factors of S. agalactiae reported herein is temperature‐dependent, and it is likely that CAMP factor directly kills the TK‐1 cells since the other two types of protein are involved in S. agalactiae cell division and the bacterial adherence to host tissues.

中文翻译：

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无乳链球菌分泌蛋白对罗非鱼培养细胞的细胞毒性

无乳链球菌分泌的毒力因子被认为能够杀死宿主组织，尤其是在升高的水温下。在罗非鱼肾（TK-1）细胞培养上测试了无乳链球菌分泌产物对罗非鱼细胞的直接作用。在四种不同的温度水平下培养细菌：22、29、32和37°C；无细胞部分通过SDS-PAGE处理; LC-MS / MS鉴定出不同的谱带。至少鉴定出三种毒力因子，Bsp，PcsB和CAMP因子，随着培养温度的升高其水平逐渐增加。随着无乳链球菌温度的升高，bsp，pcsB和cfb的表达也上调。文化。将在特定温度下培养的细菌的上清液添加到TK-1细胞培养孔中。根据无乳链球菌培养物中温度的升高，通过MTT法测定的培养细胞的形态学损伤和死亡率从上清液处理逐渐增加。这项研究表明，生产的三个毒力因子的无乳链球菌本文报道的是温度依赖性的，并且很可能是CAMP因子直接杀死TK-1细胞，因为其它两种蛋白质都参与无乳链球菌细胞分裂和细菌对宿主组织的粘附。