海水工厂化养殖大菱鲆(Scophthalmus maximus)和褐牙鲆(Paralichthys olivaceus)腹水病病原菌的分离与鉴定

ISOLATION AND IDENTIFICATION OF PATHOGENIC BACTERIA IN SWOLLEN ABDOMEN OF CULTURED TURBOT(SCOPHTHALMUS MAXIMUS) AND FLOUNDER(PARALICHTHYS OLIVACEUS)

从患腹水病大菱鲆和褐牙鲆成鱼体内分离到两株致病作用强的病原菌FS1和FS2,经人工感染实验表明菌株FS1和菌株FS2为腹水症的致病菌。采用常规的生理生化鉴定方法及梅里埃全自动微生物分析系统(VITEK32),结合分子生物学方法进行病原菌的鉴定。结果表明,菌株FS1和菌株FS2分别为迟缓爱德华氏菌(Edwardsiellatarda)和溶藻弧菌(Vibrioalginolyticus)。菌株FS116SrRNA基因序列与迟缓爱德华氏菌的同源性达99%;菌株FS2的16SrRNA基因序列与溶藻弧菌、哈维氏弧菌、副溶血弧菌等的同源性均达99%。为最终确定菌株FS2的分类地位,测定了其HSP60基因序列,进行网上同源性比对。分析结果表明,菌株FS2与溶藻弧菌的同源性达99%,而与其他弧菌HSP60基因的同源性均低于91%。这两种致病菌混合感染或分别感染均可造成养殖鲆鱼腹水病。

Turbot（ Scophthalmus maximus） and flounder（ Paralichthys olivaceus） are two members of Bothidae of Pleuronectiformes. They are rare oceanic fish species in high economic value in northern China. With the rapid development in high-density aquaculture, diseases have become a major obstacle to the cultivation of them and other aquatic animals. During 2003-2005, an outbreak of swollen abdomen in fish farms in Tianjin, China resulted in serious mortality. The suffered fish show special syndrome such as slow moving, swollen abdomen with much yellowish or sanguineous mucoid fluid, and tumid liver and kidney. Two strains of pathogenic bacteria, namely FS1 and FS2 were isolated from suffered adult fishes. Strains FS1 and FS2 were proved to be the pathogenic bacteria by the infection experiment. Strain FS2 was virulent to P. olivaceus with an LD50 at 1.05 × 10^5 cells by intramuscular injection experiment. In this research, different methods including VITEK system, traditional physiological and biochemical identification and molecule methods were used to identify the two pathogenic bacteria. The results showed that the strains were respectively identified as Edwardsiella tarda and Vibrio alginolyticus. The 16S rRNA gene sequence of Strain FS1 showed 99% similarity to E. tarda, while that of Strain FS2 shared 99% similarity with V. alginolyticus, V. hatveyi and V. parahaemolyticus. In order to identify Strain FS2, HSP60 gene partial sequence of the strain was determined. By online homological comparison, the Strain FS2 was found having 99% similarity to V. alginolyticus, while the similarity to other vibrios was less than 91%. Whether mixed infection or individual infection could result in swollen abdomen of cultured turbot and flounder.