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【目的】2013年5月广东番禺某养殖场罗非鱼出现大量死亡现象,临床症状表现为鱼体体色发黑、体表出血、鳞片脱落、鳍条溃烂等,解剖发现腹腔有大量腹水、胆囊肿大、肝呈黄色、脾脏呈暗红色。为确定病原,【方法】从具以上临床症状的病鱼组织中分离获得可疑菌株1株,编号PYS1。采用形态特征、生长特性、理化特征、16S rRNA基因序列分析等理化及分子生物学技术鉴定该菌株种类。通过人工回归感染及组织病理学研究确定该菌株的致病性,并开展药物敏感性试验筛选其敏感药物。【结果】结果表明PYS1菌株为类志贺邻单胞菌(Plesiomonas shigelloides),在16S rRNA基因序列构建的分子进化树中与其他鱼源类志贺邻单胞菌聚为一支。药敏试验结果表明该菌株已呈现多重耐药性,仅对少数检测抗生素(头孢曲松、头孢洛克和头孢唑啉等)敏感。人工回归感染结果显示PYS1菌株可使尼罗罗非鱼出现与自然发病鱼相似症状,其对尼罗罗非鱼半致死量为1.425×108CFU/尾,石蜡切片显示其对感染鱼的肠、肝、脾、肾和心脏等组织均可造成损伤。【结论】证明类志贺邻单胞菌为上述养殖场尼罗罗非鱼发病的病原,且为首次报道该菌对尼罗罗非鱼的致病性。
【Aim】 In May 2013, there was a large number of tilapia deaths in a farm in Panyu, Guangdong Province. The clinical manifestations were black body color, bleeding on the body surface, exfoliation of scales and ulceration of the fins. The abdominal cavity was found to have a large amount of ascites, Gallbladder enlargement, liver yellow, dark red spleen. To determine the pathogen, 【Method】 Suspected strains were isolated from diseased fish tissues with the above clinical symptoms and numbered PYS1. The morphological characteristics, growth characteristics, physical and chemical characteristics, 16S rRNA gene sequence analysis and other physical and chemical and molecular identification of the strain. The pathogenicity of the strain was confirmed by artificial retrograde infection and histopathology, and drug susceptibility tests were conducted to screen the sensitive drugs. 【Result】 The results showed that PYS1 strain was Plesiomonas shigelloides and clustered together with other fish species of Pseudomonas sp. In the molecular phylogenetic tree constructed by 16S rRNA gene sequence. Susceptibility test results show that the strain has shown multi-drug resistance, only a small number of test antibiotics (ceftriaxone, cefalot and cefazolin, etc.) sensitive. The results of artificial regression infection showed that PYS1 strain could cause the similar symptoms to the naturally occurring fish, with a semi-lethal dose of 1.425 × 108 CFU / tail to the nile tilapia. Paraffin sections showed that the intestinal flora of the infected fish , Spleen, kidney and heart tissue can cause damage. 【Conclusion】 It is proved that the strain of Pseudomonas choleraesuis is the causative agent of the above-mentioned Nile tilapia in farms and is the first reported pathogenicity of the strain to Nile tilapia.