中文摘要：

从团头鲂（Megalobrama amblycepnala）肠道中分离纯化到4株细菌,菌株编号为MA1～4,通过细菌镜检及培养结果表明,均为革兰氏阴性直杆状菌,在LB培养基上生长;4株细菌氧化酶试验为阴性、过氧化氢酶试验为阳性、半固体动力阳性,不能利用棉子糖、山梨醇、木糖等多种糖类,产H2S、VP试验和葡萄糖酸盐利用试验为阴性;采用数值编码鉴定,MA1为鲶鱼爱德华氏菌（Edwardsiella ictaluri）,MA2为摩氏摩根氏菌（Morganella morganii）,MA3为嗜线虫致病杆菌（Xenorhab-dus nematophilua）,MA4为弗氏志贺菌（Shigella flexneri）。进一步进行药敏试验分析显示,4株菌耐药率分别为52.2%、69.6%、95.7%、100%,均对阿奇霉素、红霉素、洁霉素、氯洁霉素、灭滴灵、头孢噻吩、先锋霉素Ⅳ、复方新诺明和甲氧咔啶具有耐药性;对利福平、氯霉素、头孢孟多、先锋必素、氧哌嗪青霉素、氨苄青霉素、庆大霉素、卡那霉素和四环素等药物敏感性不同。该研究结果对探明鱼类肠道菌群、养殖水体微生态和疾病防治具有重要参考价值。

英文摘要：

The bacteria were isolated from the intestine of Megalobrama amblycephala,the 4 strains were named MA1-4,respectively.Microscopic examination and bacterial culture results showed that 4 strains of bacteria were straight rod-shaped Gram-negative bacteria,which could grow on LB agar;based on physiological and biochemical characteristics of the strains,MA1 belonged to Edwardsiella ictaluri,MA2 belonged to Morganella morganii,MA3 belonged to Xenorhabdus nematophilua,and MA4 belonged to Shigella Flexneri.Further drug sensitivity test results revealed that the resistance rate were 52.2%,69.6%,95.7% and 100%,repectively,four strains were resistant to Azithromycin,Erythromycin,Lincomycin,Clindamycin,Metronidazole,Cefalotin,Vanguard ADM Ⅳ,Sulfamethoxazole and Methoxyl Carbazole,but the strains have different sensitivity to Rifampicin,Chloromycetin,Cefamandole,Cefoperazone,Piperacillin,Ampicillin,Gentamicin,Kanamycin,Tetracycline,etc.The results suggested that the intestine may be a natural reservoir for opportunistic pathogen in fish,thus provided a reference with the application of intestinal bacteria and prevention and control of fish diseases.