Lei Xueping, Zhao Ruoxuan, Geng Yi, Wang Kaiyu, Yang Ping Ou, Chen Defang, Huang Xiaoli, Zuo Zhicai, He Changliang, Chen Zhengli, Huang Chao, Guo Hongrui, Lai Weimin
College of Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Sichuan 611130, PR China.
Dis Aquat Organ. 2020 Nov 5;142:13-21. doi: 10.3354/dao03517.
Nocardia seriolae is the causative agent of nocardiosis in both marine and freshwater fish. Here, we report on multiple outbreaks of nocardiosis associated with elevated mortality (23-35%) in farmed largemouth bass in Sichuan, China, from 2017 to 2018. A total of 9 strains isolated from diseased largemouth bass were identified as N. seriolae by phenotypic characterization, 16S rRNA and hsp65 gene sequence analysis. The clinical signs of infected largemouth bass included hemorrhage, skin ulcers and prominent tubercles varying in size in the gill, liver, spleen and kidney. Experimental infection indicated that these isolates were the pathogens responsible for the mortalities. In vitro antibacterial activities of 12 antibiotics against N. seriolae isolates were determined as minimum inhibitory concentrations. Histopathological observation of diseased fish infected with N. seriolae showed necrotizing granulomatous hepatitis, nephritis, splenitis, epithelial hypertrophy and hyperplasia with degenerative changes of the epithelium in the gill. Large quantities of bacterial aggregates were found in the necrotic area of the granuloma by Lillie-Twort Gram stain and immunocytochemistry. Our findings indicated that N. seriolae is a serious threat to the largemouth bass Micropterus salmoides industry in Southwest China.
鰤诺卡氏菌是海水和淡水鱼类诺卡氏菌病的病原体。在此，我们报告了2017年至2018年中国四川养殖大口黑鲈中与死亡率升高（23%-35%）相关的多次诺卡氏菌病暴发情况。通过表型特征、16S rRNA和hsp65基因序列分析，从患病大口黑鲈中分离出的9株菌株被鉴定为鰤诺卡氏菌。感染大口黑鲈的临床症状包括出血、皮肤溃疡以及鳃、肝、脾和肾中大小不一的明显结节。实验感染表明这些分离株是导致死亡的病原体。测定了12种抗生素对鰤诺卡氏菌分离株的体外抗菌活性，以最小抑菌浓度表示。对感染鰤诺卡氏菌的患病鱼类进行组织病理学观察，显示坏死性肉芽肿性肝炎、肾炎、脾炎、上皮肥大和增生，鳃上皮有退行性变化。通过Lillie-Twort革兰氏染色和免疫细胞化学在肉芽肿坏死区域发现大量细菌聚集体。我们的研究结果表明，鰤诺卡氏菌对中国西南部的大口黑鲈产业构成严重威胁。
