六须鲶暴发性败血症病原菌的分离与鉴定

The isolation and identification of pathogen in northern sheatfish Silurus soldatovi suffering from fulminant septicaemia

从患暴发性败血症的六须鲶Silurus soldatovi身上分离到致病菌株(FY-024),用常规细菌培养方法对其观察,并进行生理生化特性测试。结果表明,该致病菌均符合鲶爱德华氏菌Edwardsiella ictaluri特征。为了进一步确认该致病菌的分类地位,对其进行了16S rRNA基因序列分析、遗传距离距阵及系统发育树分析,共扩增出1 417 bp基因片段(GenBank登录号为GQ924477)。系统发育结果显示,菌株FY-024与鲶爱德华氏菌的16S rRNA基因同源性达99.6%～99.9%,聚为同一分支,进一步确认致病菌是鲶爱德华氏菌。药敏试验和毒力试验结果显示,菌株FY-024对环丙沙星、恩诺沙星药物高度敏感,按Reed和Muench氏法计算LD50=1.08×106 cfu/尾。

The bacteria strain FY-024 was isolated from northern sheatfish Silurus soldatovi suffering from fulminant septicaemia and identified by conventional tests of bacterial culture,and by physiological and biochemical characteristics.The results showed that the strain FY-024 was very likely to be Edwardsiella ictaluri.16S rRNA gene of the strain was amplified,and sequenced to investigate the phylogenetic position.A fragment of 16S rRNA gene consisting of 1 417 bp was obtained,sequenced and submitted to Genbank（Accession No.：GQ924477）.Compared with that of other related bacterial species,molecular phylogenetic dendrogram was constructed according to the genetic distance.This strain was found to be shared 99.6%-99.9% of homoeology with Edwardsiella ictaluri and clustered into one clade in phylogenetic dendrogram,confirming that this strain being Edwardsiella ictaluri.In addition,the drug sensitivity showed that this strain had high sensitivity to Ciprofloxacin and Enrofloxacin,and the strain FY-024 had a LD50（50% lethal dose,LD50） of 1.08×106 cfu per fish calculated by the method of Reed and Muench in the injection challenge test.