美洲黑石斑迟缓爱德华氏菌分离、鉴定及致病性研究

养殖美洲黑石斑(Centropristis striata)发生以“内脏白点”为主要临床症状的暴发性死亡, 为明确美洲黑石斑患病原因, 对患病鱼进行了病原分离、鉴定及致病性研究, 以期为防治美洲黑石斑迟缓爱德华氏菌病提供参考依据。患病的美洲黑石斑的症状主要表现为鳃和内脏组织如脾脏及肾脏上布满白点。从患病鱼的病灶处分离纯化到一株优势致病菌株(ZS201807), 通过对该菌株形态特征、生理生化特性和16S rDNA基因测序等综合分析, 鉴定该菌为迟缓爱德华氏菌(Edwardsiella tarda)。人工感染实验证实此菌株可引起健康美洲黑石斑发病并表现出与自然发病相似的症状。利用组织切片和电镜超薄切片技术对患病美洲黑石斑鱼的肝脏、脾脏、鳃丝等6种组织进行组织病理学分析。组织病理结果显示, 脾和肾是感染较严重的主要靶器官, 脾脏组织内大量红细胞浸润, 出现严重瘀血; 鳃丝毛细血管扩张; 肾小管管腔狭窄, 肾小球肿大, 上皮细胞肿胀, 细胞空泡化。超微病理显示, 病鱼脾脏和头肾组织有大量杆状细菌积聚。药敏试验发现该菌对环丙沙星(5 μg/片)、四环素(30 μg/片)、恩诺沙星(5 μg/片)等14种药物敏感; 对青霉素(10 U/片)、阿奇霉素(15 μg/片)、丁胺卡那(30 μg/片)等13种药物耐受。证实此次养殖美洲黑石斑发病死亡的病原菌为迟缓爱德华氏菌。

ISOLATION,IDENTIFICATION AND PATHOGENICITY OF THE PATHOGENIC BACTERIUM FROM CENTROPRISTIS STRIATA

To discover the causes of sick black seabass, bacterial strain ZS201807 was isolated from the cultured Centropristis striata with the symptoms of white spots in gill and visceral organs. The biochemical and physiological characteristics of the isolated strain were studied by using conventional method, such as API 20 and 16S rDNA gene sequence. The bacteria were identified as Edwardsiella tarda. The artificial infection experiment indicated that the strain was the causative agent of sick Centropristis striata. Histopathological analysis revealed that the spleen and kidney were the main target organs with serious infection, such as a large number of erythrocyte infiltration in the spleen tissue, serious blood stasis, gill filaments capillary dilation, renal tubular cavity stenosis, glomerular enlargement, epithelial cell swelling and cell cavitation. Ultrastructural pathology showed that there was a large accumulation of rod bacteria in the spleen and head kidney tissue of the sick fish. The drug susceptibility test showed that the bacterium was sensitive to 14 kinds of drugs such as ciprofloxacin (per 5 μg), tetracycline (per 30 μg) and enrofloxacin (per 5 μg), and resistant to 13 kinds of drugs such as penicillin (per 10 U), azithromycin (per 15 μg) and amikacin (per 30 μg). It was confirmed that the pathogen of the disease and death of the black seabass was slow Edwardsiella tarda.