大口黑鲈鲁氏耶尔森氏菌的分离鉴定、主要毒力基因及致病性研究

为探明2021年3月福建某水库养殖大口黑鲈疾病暴发的原因，实验从患病大口黑鲈肝脏、肾脏、脾脏中分离优势菌，通过人工感染实验确定病原菌，并综合16S rDNA基因序列分析、生理生化和质谱特征等技术对该病原菌进行种属鉴定，同时，进行毒力基因检测、药物敏感性实验以及组织病理学观察。结果显示，从病鱼脾脏中分离获得1株优势菌并鉴定为鲁氏耶尔森氏菌；该菌株对大口黑鲈的半致死剂量为3.8×10⁵ CFU/尾；该菌株携带yrP1、yhl A、yhl B等毒力基因，对恩诺沙星、盐酸多西环素、氟甲喹、硫酸新霉素、氟苯尼考等5种药物相对敏感。组织病理学观察发现，鲁氏耶尔森氏菌的感染造成大口黑鲈肝脏、肾脏、脾脏不同程度的损伤，表现为明显的变性、坏死及炎症细胞的浸润等。本研究首次报道了鲁氏耶尔森氏菌对养殖大口黑鲈的致病性，可为养殖大口黑鲈鲁氏耶尔森氏菌病的诊断和药物防治提供参考依据。

Isolation, identification, major virulence genes and pathogenicity of Yersinia ruckeri from Micropterus salmoides

To investigate the cause of an outbreak of unknown disease occurred in cultured largemouth bass (Micropterus salmoides) in a reservoir in Fujian Province, with a cumulative mortality of over 30% in March 2021, the dominant bacterial colonies were isolated from the liver, spleen and kidney tissues of affected fish, the pathogenic bacteria was identified by artificial infection experiments, and its species was identified by physicochemical characteristics, 16S rDNA sequences, and mass spectrometry analyses. Further, virulence gene detection, drug sensitivity research and histopathological observation were carried out. A predominant bacteria strain Yersinia ruckeri was isolated from the spleen of the inffected M. salmoides. A set of virulence genes including YrP1⁺ - YhlA^{+ -} YhlB⁺ - invF^- - traC^- - traL^- - traN^- were detected by PCR from in the isolated strain, with a LD₅₀ of 3.8×10⁵ CFU per fish by intraperitoneal injection. The antibiotic sensitivity test showed that the pathogen was sensitive to enrofloxacin, doxycycline hydrochloride, flumequine, neomycin sulfate and florfenicol. Histopathological observation found that Y. ruckeri infection caused significant damages to liver, spleen, kidney and other organs of M. salmoides. The main pathologic lesions showed obvious degeneration, necrosis and infiltration of the inflammation cells. It could be included that the current research is the first report of cultured M. salmoides infected by Y. ruckeri, which will be helpful for the early diagnosis and better prevention of the disease in cultured M. psalmodies.