广东省罗非鱼主养区无乳链球菌的分离、鉴定与致病性

从广东省5个罗非鱼主养区患暴发性的罗非鱼中分离到15株菌,挑选其中的5株(不同地域、不同组织分离的菌株)进行人工感染试验,表现出自然发病的症状,确定此5株分离菌为导致罗非鱼暴发病的主要病原。通过形态学观察和生理生化实验,并结合16SrRNA基因序列分析,5株分离菌株均为无乳链球菌(Streptococcus agalactiae)。5株分离菌在形态学和生理生化实验结果上保持一致,16SrRNA基因序列同源性达98.6%～99.8%,但在致病性和对药物的敏感性上却呈现一定的差异。另外10株分离菌株通过生理生化实验鉴定也为无乳链球菌。研究表明,广东省罗非鱼流行性暴发病的病原菌主要为无乳链球菌。

Isolation, Identification and Pathogenicity of Pathogenic Bacteria of Fulminant Disease of Tilapia in Guangdong Province

Fifteen bacteria strains were isolated from the tilapia from five main tilapia culturing areas in Guangdong province where many cultured tilapia were seriously infected by the fulminant disease.Five strains which were isolated from different tissues in tilapia and different tilapia culturing areas were selected for artificial infection experiments and the test fish appeared the similar external signs of the natural infected tilapia.Therefore,five strains were confirmed as the bacteria pathogen causing the fulminant disease of tilapia.The five strains were finally identified as Streptococcus agalactiae through physiological and biochemical tests,morphology observation and the 16SrRNA gene sequence analysis.The five tested strains shared the same biochemical characteristics,the similarity of the 16SrRNA gene sequences were between 98.6%-99.8%,but the pathogenicity and the sensitivity to 23 chemotherapeutants of the five strains were different.The other ten strains were also identified as Streptococcus agalactiae by physiological and biochemical tests.Based on these results obtained,Streptococcus agalactiae may be the major pathogen of the epidemic fulminant disease of cultured tilapia in Guangdong province.