斑点叉尾鮰败血症的病原学与病理组织学观察

Etiology and Pathohistological Observation of Septicemia in Channel Catfish Ictalurus punctatus

用常规微生物分离、鉴定方法,自体质量200~500 g患典型败血症斑点叉尾鮰肝脏、肾脏组织中分离得到1株优势菌,经7 d人工感染试验证明其病原性,并观察其肝脏、肾脏、脾脏、肠道、心脏、鳃的组织病理学。经菌体形态学观察、生理生化特性结合16S rRNA、gyrB基因序列分析,鉴定该病原为嗜水气单胞菌;对病原菌进行药物敏感性试验。结果显示,该菌仅对氧氟沙星、诺氟沙星、吡哌酸、妥布霉素敏感,对卡那霉素、多黏菌素B、阿奇霉素中度敏感,其他20种药物耐药。组织病理学观察显示,肝小叶静脉淤血,肝细胞颗粒变性、空泡变性甚至局灶性坏死;肾间质广泛性淤血、出血,淋巴细胞浸润,肾小管上皮细胞变性、脱落;脾脏淋巴细胞数量减少,淤血出血;肠黏膜坏死脱落等病变。本试验确定了嗜水气单胞菌是此次疫病的主要病原,其感染引起斑点叉尾鮰多组织出血、变性、坏死,功能障碍而死亡,并为该病的防治提供理论依据。

A bacterial strain was isolated from liver and kidney of diseased channel catfish Ictalurus punctatus showing symptoms of septicemia in Neijiang city,Sichuan province,by traditional pathogen isolation methods in order to define the potential pathogens and disease control methods of the channel catfish.The pathogenicity of the strain was validated by infection test,and identified as Aeromonas hydrophila by morphological observation,physiological and biochemical characterization,and by 16S rRNA and gyrB gene sequence analysis.The antibiotic susceptibility indicated that the strain was sensitive to ofloxacin,norfloxacin,piperidic acid and tobramycin,intermediary to kanamycin,azithromycin and polymyxin B,and resistant to other drugs in the test.The histopathological observation of the diseased channel catfish showed that the diseased was characterized by congestion of hepatic lobular veins,hepatocyte granule degeneration,granular degeneration of hepatocytes vacuolar and even focal necrosis.Extensive congestion and hemorrhage of renal interstitium,lymphocyte infiltration,degeneration and exfoliation of renal tubular epithelial cells were observed in the diseased fish,and reduction in splenic lymphocyte number,congestion and hemorrhage were found as well.Furthermore,there were necrosis and exfoliation of intestinal mucosa and other pathological changes in the diseased channel catfish.It was concluded that A.hydrophila was identified as the pathogen causing the symptoms of septicemia.The findings provided theoretical basis for the prevention and treatment of the disease.