养殖鲟鱼出血症病原鲁氏耶尔森菌的分离鉴定和致病性研究

鲁氏耶尔森菌(Yersinia ruckeri)是鲑鳟鱼类和温水性鱼类肠炎红嘴病的主要病原,可引起病鱼体表出血、肠道肿胀发炎等临床症状。本研究从患出血症施氏鲟(Acipenser schrenckii)中分离到一株致病性菌株(YR-H01),生理生化鉴定和16S rRNA基因序列分析表明YR-H01株为鲁氏耶尔森菌。人工感染该菌后发病鱼表现为肛门红肿、外突明显,部分鱼鳍基部和下颌处有出血现象,内脏器官不同程度出血,且从组织中再分离的细菌特性与原感染菌相同。腹腔注射后该菌株对施氏鲟的半致死浓度为7.2×106CFU,且攻毒剂量越大,临床病症出现越快。病理组织切片显示,该菌感染鲟鱼后肝细胞发生明显病变,淋巴细胞侵润,肝索结构消失,细胞肿胀,核空泡变性或核仁边缘化。

ISOLATION, IDENTIFICATION AND PATHOGENICITY OF A PATHOGENIC BACTERIUM YERSINIA RUCKERI ASSOCIATED WITH HEMORRHAGE OF CULTURED AMUR STURGEON (ACIPENSER SCHRENCKII)

Yersinia ruckeri is a causative agent of enteric red-mouth disease or yersiniosis; it infects salmonids and several other fish species with hemorrhagic signs on body surface and in intestine. In this study, a bacterial strain YR-H01 was isolated from Amur sturgeon (Acipenserschrenckii) with hemorrhage disease and was identified as Yersinia ruckeri by analyzing biochemical reactions and 16S rRNA gene sequence. The intraperitoneally YR-H01-injected fish showed obvious haemorrhaging in anus, ?n base, lower jaw, and internal organs. The bacterial strains isolated from artificially-infected fish showed similar morphological and biochemical characteristics to those from naturally infected fish Therefore, Y. ruckeri was pathogenic to Amur sturgeon with similar clinical signs as naturally diseased fish in LD₅₀ 7.2×10⁶CFU according to the Reed-Muench method. The stronger the challenge dosage of YR-H01 strain applied, the quicker the clinical signs appeared. Pathologic observation showed that the liver cells of fish were damaged after challenged by Yersinia ruckeri, showing obvious lesions, including lymphocytes infiltration, hepatic cord disappearance, cells plumping, vacuolar degeneration, and nucleolus marginalization.