加州鲈诺卡菌病病原的分离与鉴定

Isolation and Identification of Nocardia,A Pathogen of Nocardiosis in Largemouth Bass,Micropterus salmoides

加州鲈是我国南方的重要经济鱼类养殖品种,但近年病害问题十分突出。诺卡菌已成为危害加州鲈健康养殖的重要病原,目前对该病原菌的分离鉴定及种属类型的研究尚未见报道。国内首次从患病加州鲈体内分离得到诺卡菌,并最终确定了其病原种类是鰤鱼诺卡菌Nocardia seriolea。从患病加州鲈内分离到菌株NH090627,镜检发现该菌为革兰氏阳性的分支状杆菌。生理生化鉴定结果表明分离菌株与诺卡菌属Nocardia细菌的基本特征相符。回归感染试验证实菌株NH090627即为引起此次加州鲈结节病的病原菌。对该菌株的16SrDNA进行了扩增和序列分析发现,该菌株与诺卡菌属细菌的亲缘关系较近,且与鰤鱼诺氏菌N.seriolea JCM3360的16S rDNA序列同源性最高,达到99.9%。综合上述试验结果,我们将加州鲈结节病的病原菌鉴定为鰤鱼诺卡菌。为了指导该病的防控,还对该病原菌做了一系列药敏试验,结果显示,该菌株对氯霉素、链霉素、卡那霉素、四环素等抗生素敏感,但对磺胺类和氨苄青霉素有耐药性。

Nocardiosis is a commercially important disease in cultured largemouth bass in China,causing substantial economic losses.However,the pathogen causing largemouth bass nocardiosis has not yet been isolated in China.In this study,a strain of Nocardia（designed as NH090627） was isolated from diseased largemouth bass reared in Nanhai,Guangdong.The bacteria appeared Gram-positive,bead-like or long,slender,filamentous rods in shapes.The traditional physiological and biochemical methods showed that most of the phenotypes of strain NH090627 were similar to Nocardia.Phylogeny analysis with 16S rDNA showed that the strain NH090627 was branched into the same cluster as that of other species of Nocardia,and had a higher identity with Nocardia seriolae JCM 3360T（99.9%）.Based on morphological,physiological,biochemical properties and phylogenetic analysis,the filamentous rod bacterial was identified as Nocardia seriolea.Antimicrobial susceptibility assay showed that this strain was susceptible to chloramphenicol,streptomycin,kanamycin and tetracycline,but high resistant to sulphamethoxazole and ampicillin.