无乳链球菌感染吉富罗非鱼后体内病原菌的动态分布

Dynamic distribution of pathogenic bacteria in GIFT infected artificially with Streptococcus agalactiae

【目的】研究吉富罗非鱼感染无乳链球菌后其体内主要器官组织中病原菌的分布及消除规律,为罗非鱼无乳链球菌病的诊断和药物防治提供科学依据。【方法】对吉富罗非鱼进行人工腹腔注射无乳链球菌（HN016菌株）,分别在感染后3、6、12、18、24、48、72、96、120、144、168 h和10、15、20、30 d,随机选取未死亡罗非鱼取样（脑组织、肝脏、前肾和脾脏）划线接种于鸡血培养基上,28℃培养12 h后统计菌落数量。【结果】人工注射感染HN016菌株3 h后,吉富罗非鱼未出现发病症状,但在其脑组织、肝脏、前肾和脾脏均可分离出病原菌;感染18 h后进入发病高峰期,从其肝脏、脾脏分离出的菌落数量明显多于脑组织和前肾,之后各组织的病原菌落数量持续增长并在48～72 h间趋于稳定;感染72 h后各组织分离出的菌落数量逐渐减少;感染10 d后从存活吉富罗非鱼的脑组织已分离不到病原菌,感染20 d后存活鱼体的脑组织、肝脏、前肾和脾脏均未分离出无乳链球菌。【结论】吉富罗非鱼感染无乳链球菌（HN016菌株）的发病死亡高峰期在感染后48～72 h,而无乳链球菌在吉富罗非鱼体内的代谢周期为20 d,因此养殖生产中应注意发病高峰期间的水体消毒及减少饵料投喂。

[Objective]The present experiment was conducted to investigate distribution and elimination law of bacteria in major organ of genetic improvement of farmed tilapia （GIFT） which was artificially infected with Streptococcus agalactiae, in order to provide theoretical references for diagnosis and cure of tilapia infected with S. agalaetiae. [Method]The GIFT was infected with S. agalactiae HN016 via intraperitoneal injection, and after 3, 6, 12, 18, 24, 48, 72, 96, 120, 144, 168 h and 10,15,20,30 d, the brain, liver, pronephros and spleen were collected randomly from survival GIFT, respectively. Then these collected samples were inoculated into chicken blood medium, and the plate bacteria counting method was used to count quantity of pathogenic bacteria. [Result]The results showed that GIFT had no disease symptom after being infected artificially with HN016 strain for 3 h, however the pathogenic bacteria could be isolated from brain, liver, prouephros and spleen. The peak incidence oceured at 18 h after infection, and the numbers of bacteria isolated from liver and spleen were significantly higher than those from pronephros and brain, respectively. And then the number of pathogenic bacteria gradually increased and later kept stable at 48-72 h after infection. After 72 h, the number of pathogenic bacteria was found to decrease gradually. Furthermore, the pathogenic bacteria could be hardly isolated from brain on 10 d after infection, and could not be found on 20 d in brain, liver, pronephros and spleen. [Conclusion]The peak death incidence of GIFT infected with S. agalactiae（HN016 strain） occurs at 48-72 h after infection, and the metabolic cycle of S. agalactiae was 20 d. Therefore, the more attention should be payed to disinfect water and reduce feeding at the peak of death in aquaculture.