海南养殖罗非鱼(Oreochromis niloticus)致病链球菌的分离、鉴定及其药敏试验

采用常规的形态及生理生化特性检验、API20strep快速鉴定及分子生物学等方法,对引起2009年海南罗非鱼大规模死亡的病原菌进行了致病性、表型生物学,分子生物学及药敏试验的系统研究。结果表明,2株分离菌均为无乳链球菌,对罗非鱼具有很强的致病性。分离菌16SrRNA基因序列(GenBank登录存取号分别为GU363869和GU363870)与其它链球菌的16SrRNA基因同源性相似性在96.5%—100%之间,所测2株病原菌16SrRNA基因之间的同源性为100%。16SrRNA基因构建的系统进化树表明,2株病原菌均与无乳链球菌聚类。药敏试验结果表明,分离菌株对头孢类药物、阿莫西林、强力霉素等27种试验药物较敏感,对复方新诺明、卡那霉素等11种试验药物不敏感,对庆大霉素的敏感性不同。

ISOLATION, IDENTIFICATION AND DRUG SENSITIVITY TEST OF PATHOGENIC STREPTOCOCCUS FROM TILAPIAS OREOCHROMIS NILOTICUS CULTURED IN HAINAN

Two strains of bacteria, HN090816-1 and HN090816-2, were isolated from diseased tilapia Oreochromis niloticus cultured in Hainan, and were confirmed to be pathogenic by recurrent infections. They were identified as Streptococcus in regular physiological and biochemical analyses. With the API 20 strep technique, they were recognized as Streptococcus agalaciate, which were of 99.9% homology to S. agalaciate. In order for further confirmation on the molecular level, 16S rRNA gene were sequenced, their sequence accession number in GenBank being GU363869 and GU363870 respectively. Sequences analysis of 16S rRNA gene showed that they were very similar to other Streptococcus, and their nucleotide homology were between 96.5% and 100%. The nucleotide homology of 16S rRNA gene between the two isolates were 100%. Phylogenetic tree of Streptococcus based on 16S rRNA gene showed that strains HN090816-1 and HN090816-2 clustered together with S. agalaciate. Therefore, strains HN090816-1 and HN090816-2 were identified as S. agalaciate. Their sensitivities to 48 kinds of antimicrobial drugs were determined. The result showed that the two isolates were both highly sensitive to 27 antibiotics, such as Cephalosporin Drugs, amoxicillin and doxycycline, and were both resistant to 11 antibiotics, such as cotrimoxazole and kanamycin; while they showed different sensitivity to gentamicin.