丝足鲈致病性诺卡氏菌的鉴定及系统发育分析

Identification and Phylogenetic Analyses of Pathogen Nocardia sp Islated from Giant Gourami(Osphronemus gorami)

为查明养殖的丝足鲈内脏结节病的病因,由患病丝足鲈内脏分离到菌株1214,并对该菌进行了鉴定及致病性验证。结果显示所分离菌株1214革兰氏染色呈阳性,长短不一,为丝状分支状杆菌;回归感染试验证实菌株1214为引起此次丝足鲈结节病的病原菌;生理生化鉴定结果表明菌株1214与诺卡氏菌属细菌的基本特征相符;对该菌株的16SrDNA序列分析显示其与鱼诺卡氏菌JCM 3360的16SrDNA序列同源性最高,达到99.9%。综合以上结果最终确定此次丝足鲈结节病的病原为鱼诺卡菌。药敏试验结果显示,该菌株对红霉素、氟苯尼考、链霉素、强力霉素、阿奇霉素等抗生素敏感,但对磺胺类和青霉素有耐药性。

A strain of Bacterium（designed as 1214）was isolated and identified from the visceral of diseased tropical ornamental fish giant gourami（Osphronemus gorami）reared in Tianjin.The strain 1214 was found to be Gram-positive,branching,bead-like or long,slender,and filamentous rods in shapes.The infection experiments indicated that the isolated bacterium was pathogen responsible for the mortality.The traditional physiological and biochemical methods showed that most of the phenotypes of strain 1214 were similar to Nocardia,and phylogeny analysis with 16SrDNA showed that the strain 1214 was branched into the same cluster as that of other species of Nocardia,and had a higher identity with N.seriolae JCM3360T（99.9%）.Based on the symptom of diseased fish and the growth characteristics,morphological,physiological,biochemical properties and phylogenetic analysis,the filamentous rod bacterium was identified as N.seriolea.Antimicrobial susceptibility assay revealed that this strain was susceptible to florfenicol,streptomycin,erythromycin,doxycycline and azithromycin,but high resistant to sulphamethoxazole and penicillin.