大口黑鲈鰤诺卡菌的分离鉴定及其感染的病理损伤研究

Isolation and Identification of Nocardia seriolae from Large-mouth Bass (Micropterus salmoides) and Pathological Lesions of Its Infection

【目的】近年来,四川养殖大口黑鲈(Micropterus salmoides)流行一种以体表溃疡、内脏器官出现白色结节为主要病症的疫病。本研究对其病因及病理损伤特点进行分析。【方法】进行病原菌分离、人工感染、病原菌理化特性分析和16S rDNA与hsp65基因(65-ku heat shock protein gene)序列分析,同时进行药敏试验与病理损伤观察。【结果】从病鱼内脏分离到3株具有弱抗酸性的G^+丝状杆菌,人工感染试验证实了分离菌的病原性,其理化特性与鰤诺卡菌(Nocardia seriolae) ATCC43993一致;在以16S rDNA序列与hsp65序列构建的系统发育树上,分离菌与鰤诺卡菌聚为一族,3株分离菌都被鉴定为鰤诺卡菌。3株分离菌对多西环素、红霉素和庆大霉素均敏感,对青霉素和头孢噻呋均耐药,但在对恩诺沙星、氧氟沙星与复方新诺明的敏感性上存在一定差异。鰤诺卡菌感染大口黑鲈的组织病理损伤主要表现为:全身多组织器官内出现大小不等的慢性肉芽肿结节,尤以鳃、肝、脾、心、肾和头肾损伤严重,且组织切片革兰氏染色显示肉芽肿中有大量病原菌分布。【结论】鰤诺卡菌感染是此次大口黑鲈发病的病因,造成大口黑鲈多组织器官形成肉芽肿结节,且结节内有大量病原菌。

[Purpose]In recent years, a serious infectious disease characterized by skin ulcers and white nodules in visceral organs emerged in Micropterus salmoides farms in Sichuan. Therefore, we analyzed its etiology and pathological characteristics. [Method]The isolation of pathogenic bacteria, artificial infection, physical and chemical characteristics of the isolated bacteria, 16S rDNA and hsp65 gene sequence analysis, drug sensitivity test and pathological damage observation were carried out in this study. [Result]Three strains of G+ filamentous bacteria with weak acid resistance were isolated from the viscera of diseased fish. Artificial infection test confirmed the pathogenicity of the isolated bacteria, and their physical and chemical characteristics were identical with the type strain(ATCC43993). In the phylogenetic trees based on 16S rDNA and hsp65 sequence, 3 isolates and N.seriolae ATCC43993 constituted a branch, and 3 isolates were identified to be N. seriolae. 3 isolates were sensitive to doxycycline, erythromycin and gentamicin, and resistant to penicillin and ceftiofur,and there were some differences in enrofloxacin, ofloxacin and trimethoprim/sulfemethoxazole. Histopathological injuries of large mouth perch infected with N. serioloe mainly manifested as chronic granulomatous nodules of varying sizes in multiple tissues and organs of the whole body. Typical nodules were generally divided into three layers: caseous necrosis, epithelioid cells, lymphocytes and fibroblasts peripherally. And gill, liver, spleen, heart, kidney and head kidney were severely damaged.A large number of pathogenic bacteria were distributed in granuloma. [Conclusion]N. seriolae infection is the cause of the largemouth bass, which causes the formation of granulomatous nodules in many tissues and organs, and there are a large number of pathogenic bacteria in the nodules.