BALB/c小鼠用于评价尼罗罗非鱼无乳链球菌毒力的研究

实验采用BALB/c小鼠作为实验动物,旨在建立尼罗罗非鱼无乳链球菌毒力测定的BALB/c小鼠模型。BALB/c小鼠经腹腔注射尼罗罗非鱼源无乳链球菌建立感染模型,比较了尼罗罗非鱼源无乳链球菌分别感染尼罗罗非鱼和小鼠的LD_(50)差异,分别测定了不同毒力尼罗罗非鱼无乳链球菌对尼罗罗非鱼和小鼠的毒力。结果显示,小鼠经腹腔注射无乳链球菌,在24 h内出现死亡现象,且对小鼠脑、肝脏、脾脏、肾脏等组织造成损伤。3次测定尼罗罗非鱼无乳链球菌TFJ0901对尼罗罗非鱼和小鼠LD_(50)分别为7.7×10~7、2.2×10~8、3.5×10~9 CFU/mL和405、361、419 CFU/只。将无乳链球菌TFJ0901和THN0901感染尼罗罗非鱼(1.0×10~7 CFU/mL)和小鼠(100 CFU/只),尼罗罗非鱼和小鼠存活率分别为100%、6.7%±5.8%和100%、0,其存活率都具有显著性差异。将无乳链球菌TFJ0901和TFJ-F感染尼罗罗非鱼(3.0×10~8 CFU/mL)和小鼠(2 500 CFU/只),尼罗罗非鱼的存活率分别为73.3%±11.5%和80.0%±10.0%,存活率差异不显著,小鼠存活率分别为13.3%±11.5%和100.0%,存活率具有显著性差异。研究表明,本实验成功建立了BALB/c小鼠作为尼罗罗非鱼源无乳链球菌毒力测定的稳定模型,测定不同毒力的尼罗罗非鱼源无乳链球菌对小鼠毒力与对尼罗罗非鱼毒力一致,且该模型能够区分尼罗罗非鱼模型难以区分的毒力相近的无乳链球菌。

Virulence evaluation of Streptococcus agalactiae isolated from tilapia(Oreochromis niloticus) using BALB/c mice

Streptococcus agalactiae is one of the major pathogens of tilapia (Oreochromis niloticus). At present, the virulence of strains was evaluated mainly by comparing the median lethal dose (LD₅₀) to tilapia. However, tilapia as experimental animals for evaluation of the virulence of S. agalactiae was often unstable. In this experiment, BALB/c mice were used as experimental animals, in order to establish a method for the determination of virulence of S. agalactiae. BALB/c mice were injected intraperitoneally with tilapia Streptococcus agalactiae to establish an infection model. The LD₅₀ of Streptococcus agalactiae to tilapia and mice were tested 3 times and the virulence of different Streptococcus agalactiae to tilapia and mice was determined. Results show that:by intraperitoneal injection, S. agalactiae can cause the death of mice within 24 hours. S. agalactiae could damage brain, liver, spleen, kidney and other tissues in mice. The LD₅₀ of S. agalactiae to tilapia and mice 3 times was 7.7×10⁷, 2.2×10⁸, 3.5×10⁹ CFU and 405, 361, 419 CFU, respectively. When S. agalactiae TFJ0901 and THN0901 infected tilapia (1.0×10⁷ CFU) and mice (100 CFU), the survival rates of tilapia and mouse were 100.0%, 6.7%±5.8%, and 100.0%, 0%, respectively, both of which were significantly (P<0.05) different. When S. agalactiae TFJ0901 and TFJ-F infected tilapia (3.0×10⁸ CFU) and mice (2 500 CFU), the survival rates of tilapia were 73.3%±11.5% and 80.0%±10.0%, respectively, which were not significantly (P > 0.05) different from each other, while the survival rates of mice were 13.3%±11.5% and 100.0%, respectively, which were of significant (P<0.05) difference. Taken together, BALB/c mice were successfully established as a stable model for virulence determination of S. agalactiae in tilapia. The determination of the virulence of different S. agalactiae in mice is consistent with tilapia, and this model was able to distinguish S. agalactiae with similar virulence that was difficult to be distinguished by using tilapia model.