长薄鳅恶臭假单胞菌的分离鉴定及其感染的病理损伤

恶臭假单胞菌(Pseudomonas putida)是广泛分布于土壤、水体中的一种条件致病菌,可感染两栖类、鱼类和甲壳类等多种水生动物。2017年8月,四川省西昌市某养殖场的长薄鳅出现一种以体表溃烂、鳍条出血为主要特征的传染病。为探究其病因,本研究进行了病原菌分离、人工感染、分离菌表型特征测定、16S rRNA与gyrB基因序列分析。从病鱼肝、脾、肾中分离到优势菌株(BMH170820),人工感染试验证实了其病原性。根据其菌落形态、生理生化特性,结合16S rRNA与gyrB基因序列分析鉴定其为恶臭假单胞菌。组织病理学观察发现,其感染长薄鳅对鳃、肾、肝、心、脾与消化道等多处组织器官造成损伤,表现出明显的变性、坏死和炎症反应,致全身多器官功能障碍而死亡。药物敏感试验显示,该菌对新霉素、氧氟沙星以及强力霉素等敏感,而对阿莫西林、头孢氨苄与氟苯尼考等耐药。

Isolation and identification of Pseudomonas putida from Leptobotia elongate and pathological lesions of its infection

Pseudomonas putida is a conditional pathogen that widely distributed in water and soil, which can infect aquatic animals such as amphibians, fish and crustaceans. During August in 2017, a serious infection that characterized by ulceration of body surface and bleeding of fins occurred in a loach farm located in Xichang, Sichuan Province of China. To determine the etiology of this outbreak, pathogen isolation, experimental infection, physical and chemical characteristics of isolated bacteria and sequence analysis of 16S rRNA and gyrB gene were carried out. Results showed that a gram-negative, rod-shaped bacillus (designated as BMH170820) was isolated from the diseased fish and its pathogenicity were confirmed by experimental infection test for its pathological changes were consistent with that of natural infection. Based on the colony morphology, physiological and biochemical characteristics, combined with 16S rRNA and gyrB gene sequence analysis, Pseudomonas putida was confirmed as the causative factor of this outbreak. Histopathological observation revealed that Pseudomonas putida infection in Leptobotia elongate were followed as obvious degeneration, necrosis and inflammation in gill, kidney, liver, heart, spleen and digestive tract, the extensive and serious multiple organ dysfunction might lead to the death of Leptobotia elongate. Drug sensitivity tested results showed that this isolated strain of Pseudomonas putida was sensitive to neomycin, ofloxacin, doxycycline, etc, but resistant to amoxicillin, cefalexin and florfenicol.