3株牛支原体对牛体的试验感染研究

Study on Experimental Infection of Three Mycoplasma bovis Isolates in Cattle

为了明确从患有严重呼吸道症状的病/死牛肺部分离到的3株牛支原体的特征,本试验采用回归本体动物的攻毒试验方法,将12头4~7月龄犊牛随机分为4个组,每组3头,感染组(W70组、Q3组和JX02组)分别注射分离到的3株牛支原体(W70株、Q3株和JX02株)的液体培养物,阴性对照组注射培养用的肉汤培养基,通过临床症状、组织病理学和血清学方法分析3株牛支原体对动物机体的致病性和免疫特性。结果显示,3株牛支原体分离株感染犊牛后,均能引起犊牛体温升高、呼吸频率加快和明显的呼吸道症状;剖检及组织病理学检查均可见病理变化,其中W70株引起的病变最为明显;酶联免疫吸附试验(ELISA)检测血清抗体发现,感染后15 d牛支原体抗体水平达到峰值。结果表明,3株牛支原体分离株中W70株毒力最强,感染犊牛后能引起特征性的临床症状和病理变化,同时能诱导较好的免疫反应,可作为抗牛支原体疫苗的候选菌株。

To characterize three Mycoplasma bovis(M. bovis) isolates from the lungs of sick/dead cattle with severe respiratory symptoms, this study utilized regression of attack of the animal body poison test involving 12 calves aged 4-7 months in 4 groups, with 3 calves in each group. The infected groups(W70 group, Q3 group and JX02 group) were injected with liquid cultures of three individual M. bovis isolates(W70 strain, Q3 strain and JX02 strain), while the negative control group was injected with broth culture medium. The pathogenic differences and immune characteristics of three M. bovis isolates were analyzed according to clinical symptoms, histopathology and serology. The results showed that all three M. bovis isolates were pathogenic to calves, causing increased body temperature, accelerated respiratory rate and obvious respiratory symptoms. Histopathological examination revealed obvious pathological changes in all infected calves, and the lesions in the W70 group were the most severe. Enzyme-linked immunosorbent assay(ELISA) detected specific antibodies in serum, with the antibody levels to bovine mycoplasma peaking at about 15 days after infection. Thus, being the most virulent among three M. bovis isolates, W70 is capable of causing characteristic clinical symptoms and pathological changes and inducing strong immune response in experimental calves, and deserves to be assessed as a vaccine candidate against M. bovis infection.