海南罗非鱼无乳链球菌分离鉴定及其特性研究

从海南省患暴发性疾病的罗非鱼(Tilapia)上分离出1株细菌HNLFYL4,对分离菌株进行了鉴定及致病性和药物敏感性研究.通过形态学观察和生理生化鉴定,结果显示,分离菌株为无乳链球菌(Streptococcus agalactiae).对分离菌株的16S rRNA基因进行PCR扩增和测序,所得序列已登录到GenBank,登录号为HQ645983,与GenBank中收录的链球菌16S rRNA 基因进行比对并构建系统进化树,结果表明,分离菌株的16S rRNA基因序列与无乳链球菌同源性高达100%,进一步确定分离菌株为无乳链球菌.人工感染显示分离菌株对小白鼠和罗非鱼均具有致病性,对小白鼠的LD50为1.0×104 CFU/mL,对体重为500g±20g的罗非鱼的LD50为1.729×109CFU/mL.分离菌株对氯霉素、青霉素G、呋喃妥因等敏感,对丁胺卡那、链霉素、卡那霉素等不敏感.

Isolation, identification and characterization of Streptococcus agalactiae in tilapia in Hainan

One pathogenic bacteria strain HNLFYL4 was isolated from diseased tilapia in Hainan.In this study,bacteria isolation and identification,artificial infection tests were used for analysis of the cause of the severe disease.The isolate was identified as Streptococcus agalactiae based on morphology,cultural performance and biochemical characteristics.The 16S rRNA gene sequence of the isolate was amplified and compared with those of other Streptococcus retrieved from GenBank.The 16S rRNA gene sequence of the isolate had the most homology with that of S.agalactiae in GenBank.The phylogenetic tree of Streptococcus showed that the isolate was clustered together with S.agalactiae.16S rRNA gene sequence analysis further proved that the isolate belonged to S.agalactiae.The virulent tests were carried out by using the pure culture of the bacteria artificially infected tilapia and mouse.The isolate was pathogenic to tilapia and mouse.LD50 was 1.0×104CFU/mL to mouse and 1.729×109CFU/mL to tilapia.Drug sensitivity experiment showed that the isolate was highly sensitive to chloramphenicol,penicillin G,nitrofurantoin,etc,but was insensitive to amikacin,streptomycin,kanamycin,etc.