卵形鲳鲹结节病病原的分离与鉴定

从湛江港、阳江闸坡海水网箱养殖的患结节病卵形鲳鲹(Trachinotus ovatus)中分离一株细菌,回归感染结果证明该菌是引起卵形鲳鲹结节病的病原,对卵形鲳鲹半致死浓度为45 g-1。该菌株呈革兰阳性,好氧,具有弱抗酸性,菌体呈短杆状或细长分枝状,过氧化氢酶阳性,氧化酶阴性,还原硝酸盐,不水解酪素、黄嘌呤、酪氨酸、淀粉、明胶,以柠檬酸盐为唯一碳源生长。对其16S rDNA序列作Blast分析,构建系统进化树。结果表明,该菌株与诺卡氏菌属的菌株亲缘关系最近,且与鰤鱼诺卡氏菌(Nocardia seriolea JCM 3360T)的16S rDNA序列同源性高达99%。综合患病鱼的症状及病原菌形态、生理生化特性及16S rDNA序列的结果,该菌被鉴定为鰤鱼诺卡氏菌(N.seriolea)。

Isolation and Identification of the Pathogen Causing Sarcoidosis of Trachinotus ovatus

A pathogenic bacterium was isolated from sarcoid fish,Trachinotus ovatus cultured on seawater cage in Zhanjiang Harbour and Yangjiang Zhapo.Experimental recurrent infection indicated the isolated bacterium was responsible for sarcoidosis of T.ovatus,and the LD50 of the bacterium to T.ovatus was 45 CFU/g.The bacteria were aerobic,Gram-positive,weak acid-fast,bead-like or long,slender,filamentous rods,catalase-positive,oxidase-negative,and could reduce nitrate and aesculin but not degrade xanthine,tyrosine,casein,starch,gelatin.It could utilize the citrate as sole carbon source but not mannitol,arabinose and sorbitol.An almost complete 16S rDNA gene sequence of the bacteria was determined following PCR amplification and sequencing.The high similarity level of 16S rDNA sequence with Nocardia seriole is up to 99%.Based on the symptom of diseased fish and the morphological,physiologica,biochemical properties and Phylogenetic Analysis,the pathogenic organism was identified as N.seriolea.