尼罗罗非鱼致病性类志贺邻单胞菌(Plesiomonas shigelloides)的分离鉴定及其病理学观察

Identification and pathological observation of a pathogenic Plesiomonas shigelloides strain isolated from cultured tilapia(Oreochromis niloticus)

摘要:

摘要:【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。

Abstract:

Abstract:［Objective］A mass mortality of tilapia broke out in an aquaculture farm in Panyu，Guangdong Province in May，2013．Affected fish showed blackening of body color，haemorrhageing on surface，scales shedding，fin rotting，and the presence of yellow liver，dark red spleen，enlarged gallbladder and ascitic fluid in the abdominal cavity．The purpose of this research was isolating and identifying the pathogen． ［Methods］We isolated a suspicious bacteria strain PYS1 from diseased fish with significant pathological signs．The homology of 16S rRNA gene sequence of strain PYS1 and its morphological，cultural，and physical and chemical characteristics were studied for its identification．Its pathogenicity was investigated by recursive infection experiment and histopathological study．Its effective medicines was screened by antibiotic sensitive test．［Results］The results showed that strain PYS1 was Plesiomonas shigelloides clustered with P．shigelloides strains isolated from other fishes in the molecular phylogenetic tree of 16S rRNA gene sequences．Strain PYS1 was multiple drug resistant and only sensitive to a small part of 31 tested antibiotics (e.g.，ceftriaxone，cefaclor，cefazolin，etc.)．The symptoms of tilapia (O. niloticus) artificially infected with strain PYS1 were similar with natural infected fish．The half lethal dose (LD50) of strain PYS1 to tilapia was 1.425×108 CFU per fish． Paraffin sections showed intestine，liver，spleen，kidney and heart tissue injury caused by the strain．［Conclusion］ Our study demonstrated that P. shigelloides was the pathogen of cultured tilapia in the aquaculture farm and first reported its bacterial pathogenicity on Nile tilapia.