无乳链球菌感染尼罗罗非鱼的脑膜炎模型

目的：脑膜炎是罗非鱼无乳链球菌病的特征性临床症状,建立罗非鱼无乳链球菌脑膜炎模型,并制定相应的临床症状及组织病理学评分系统,对研究罗非鱼无乳链球菌病的致病机制具有十分重要的意义。方法：将健康罗非鱼43尾,随机分为4组：对照组(n=10)和试验组(n=33)。3组试验组根据不同感染剂量分为：10₆cfu组(n=11)、10₇cfu组(n=11)、10₈cfu组(n=11)。试验组分别将10₆、10₇、10₈CFU的无乳链球菌菌液腹腔注射罗非鱼复制脑膜炎模型。对感染罗非鱼的临床症状、剖检病变、脑组织(端脑、中脑、小脑、延脑)病理学进行判定,并结合细菌学检测,按照拟定的评分系统评价各组脑膜炎的造模效果,确定最佳造模方案。结果：各试验攻毒组罗非鱼感染后2天均出现不同程度死亡,未见明显神经症状。感染3天后鱼体开始出现异常活动的神经症状及突眼、角膜混浊等病理变化。病理组织学观察可见：蛛网膜下腔和脑软膜上有大量炎性渗出和染成蓝紫色微细颗粒的细菌团块,脑膜充血、水肿、疏松、增厚,有大量的中性白细胞等炎性细胞浸润；脑实质基质疏松水肿,呈海绵状；脑组织炎性细胞浸润,胶质细胞增生等软脑膜炎、脑膜脑炎症状。比较各组得分发现,10₇CFU组的无乳链球菌攻毒罗非鱼造模效果最好：临床症状显著而组内罗非鱼差异性最小,组织病理学观察患病罗非鱼病情和缓适中、利于观察研究。结论：使用10₇CFU无乳链球菌腹腔攻毒罗非鱼可在第3天成功构建脑膜炎模型,造模率为100%。

Oreochromis niloticus model of meningitis in Streptococcus agalactiae infection

The meningitis was the characteristic clinical manifestation in Nile tilapia(Oreochromis niloticus) infected by Streptococcus agalactiae. To know the degree and extent of inflammation as well as the presence of necrosis in the brain,we build an intraperitoneal infection model and develop a new clinical and histopathological scoring system for S.agalactiae in Nile tilapia.43 healthy nile tilapias,were randomly divided into 4 groups:control group(n=10),low dose group:1.0×10⁶cfu group(n=11),middle dose group:1.0×10⁷cfu group(n=11),high dose group:1.0×10⁸cfu group(n=11).Clinical symptoms and cerebral histopathological changes(cerebrum,optical lobe,cerebellum and medulla oblongata included)was oberserved in our study,we scored these three groups and obtained the best one.The infected nile tilapia died in second day post infection,however,neurological symptoms were not apparently observed in the dead fish.Survivors developed constant aberrant swimming,exophthalmia and corneal opacity.According to microscopical examination of four regions of the brain,large amount of bacteria stained bluish violet colonized the subarachnoid space and cerebral pia mater.Histopathology revealed the changes of leptomeningitis and meningoencephalitis,including congestion/hemorrhage,edema,loose and thickening in meninges,inflammatory cell neutrophilic leukocytes infiltration,superficial periplast of brain inflammatory cell infiltration and lysis spongy-structure,gliocyte hyperplasiain,and so on.Compared with the scores,we found that the group of 1.0×10⁷cfu was the best dosage,which showed significant clinical symptoms,the minimum diversity value and the condition of the sick fish contributed to the observational study.We chose the dose of 1.0×10⁷cfu to inject nile tilapia intraperitonealy to develop a model of S.agalactiae meningitis with the 100% success rate on the third day post infection.