中文摘要：

利用营养琼脂、MaC培养基从草鱼肠道中分离到3株细菌,暂时编号为TC-1、TC-2和TC-3,通过形态学观察、生理生化特征、药敏试验、动物试验、构建系统发育进化树及PCR-SSCP分析等系统鉴定,结果表明3株菌株均为弗氏柠檬酸杆菌（Citrobacter freundii）,其中TC-2菌株对小鼠、斑马鱼有致病性;3株杆菌均对头孢噻肟、头孢曲松、洛美沙星、诺氟沙星等多种药物敏感;系统发育分析表明,3株弗氏柠檬酸杆菌16S rDNA序列与DSM30039模式株同源性分别为99.59%、99.47%和99.53%,且位于系统发育树的同一分支;进一步采用V3区PCR-SSCP分析结果显示弗氏柠檬酸杆菌SSCP图谱中菌株间带型存在差异。

英文摘要：

The bacteria were isolated from intestine in grass carp（Ctenopharyngodon idellus） using nutrient agar and MaC medium,designated temporarily as TC-1,TC-2 and TC-3,and identified with morphological observation,physiological and biochemical characteristics,drug sensitive test,animal test,established phylogenetic tree,as well as PCR-SSCP analysis.The results showed that all 3 strains were Citrobacter freundii（Cf）.Animal tests showed that TC-2 strain was lethal to mice and zebrafish,respectively.Drug sensitivity test analysis revealed that 3 strains were sensitivity to cefotaxime,ceftriaxone,lomefloxacin,norfloxacin,and many others.The phylogenetic analysis showed that 16S rDNA sequence of the 3 strains had homology to the typical strain DSM 30039 at 99.59%,99.47% and 99.53% respectively,and they located on the same branch of the phylogenetic tree.Further analysis results adopting V3 region of PCR-SSCP showed there were differences among SSCP atlases of Cf strains.