山豆根多糖对人工感染罗非鱼链球菌病的预防效果

Preventive effect of Sophora subprosrate polysaccharide on Streptococcosis of tilapia

试验研究山豆根多糖(SSP)对罗非鱼链球菌病的预防效果。从形态学、生化鉴定和双重PCR鉴定无乳链球菌GX107,测定LD_(50)。将罗非鱼分为6组(0.1%SSP、0.2%SSP、0.4%SSP、0.4%APS、无乳链球菌感染组、空白对照组),每组4个重复,每个重复20尾鱼。试验组饲喂混有不同剂量(0.1%、0.2%、0.4%)SSP的饲料,黄芪多糖(APS)对照组饲喂含0.4%黄芪多糖的饲料,无乳链球菌感染组和空白对照组投喂基础饲料。试验组和感染组以10倍的LD_(50)浓度的无乳链球菌GX107腹腔注射,空白对照组注射等量生理盐水,计算各组保护率和死亡率。结果显示,该菌在BA血平板上,出现β溶血环,在BHIA培养基上出现灰白或白色湿润凸起菌落,过氧化氢酶试验为阳性,双重PCR鉴定为无乳链球菌。感染无乳链球菌的罗非鱼肝脏、脾脏、肾脏、胆不同程度地水肿,LD_(50)为6.61×10^(5)CFU/mL。10倍LD_(50)浓度的无乳链球菌感染罗非鱼,死亡率为85.71%,添加SSP可极显著降低死亡率(P<0.01),其中0.2%的SSP保护率最高,为61.9%。研究表明,不同剂量的SSP对链球菌感染的罗非鱼能有着不同程度保护效果,可以有效降低罗非鱼感染无乳链球菌后的死亡率。

The experiment studied the effect of Sophora subprosrate polysaccharide(SSP)on Streptococcosis of tilapia.Streptococcus agalactiae GX107 was identified by morphology,biochemistry and double PCR,and LD_(50)was determined.Tilapia were divided into six groups(0.1%SSP group,0.2%SSP group,0.4%SSP group,0.4%APS group,Streptococcus agalactiae infection group and blank control group),with four replicates in each group and 20 tulapia in each replicate.The tilapia in experimental group were fed with different doses(0.1%,0.2%and 0.4%)of SSP feed,tilapia in APS control group was fed with 0.4%APS feed,tilapia in Streptococcus agalactiae infection group and blank control group were fed with basic feed.The experimental group and infection group were intraperitoneally injected with Streptococcus agalactiae GX107 with 10 times LD_(50)concentration,and the blank control group was injected with the same amount of normal saline.The results showed that the bacteria appearedβHemolytic ring on BA blood plate,grayish-white or white moist convex bacterial colony appeared on BHIA culture medium,catalase test was positive,double PCR amplification of the target band identified as Streptococcus agalactiae.The clinical symptoms were edema of liver,spleen,kidney and gallbladder,LD_(50)was 6.61×10^(5) CFU/mL.The mortality of tilapia infected by Streptococcus agalactiae with 10 times LD_(50)concentration was 85.71%.SSP could significantly reduce the mortality(P<0.01),and the protection rate of 0.2%SSP was the highest,which was 61.9%.The experiment indicates that SSP at different doses can protect tilapia infected by Streptococcus agalactiae to different degrees,and can effectively reduce the mortality of tilapia infected with Streptococcus agalactiae.