养殖大菱鲆病原菌——杀鲑气单胞菌无色亚种的分离鉴定和组织病理学研究

Isolation and Identification of Bacterial Pathogen:Aeromonas salmonicida subsp.achromogenes in Cultured Turbot and Histopathological Study

自然发病的养殖大菱鲆幼苗出现口部周围皮下出血,肝脏灰白色并萎缩坏死的症状。从肝脏中分离纯化得到优势菌株,定名为db14。该菌株在LB培养基上生长较缓慢,早期菌落稍隆起,白色,质地较硬;人工感染试验证实对大菱鲆有较强的致病性,其半数致死剂量LD50为2.75×103cfu/g;生理生化特征测定显示其与杀鲑气单胞菌无色亚种(Aeromonas salmonicidasubsp.achromogenes)相似度最高;细菌16S rDNA序列测定后在GenBank中进行序列比对分析,结果与杀鲑气单胞菌无色亚种的序列同源性最高,为100%。综合上述结果,确定该菌株为杀鲑气单胞菌无色亚种。该菌株对复达欣、菌必治、丁胺卡那霉素和氯霉素等较为敏感。通过对人工感染菌株db14的大菱鲆组织切片观察,发现病鱼的肝脏、肾脏、脾脏、肠道等器官的组织均有明显的病理变化,而心脏和脑未发现明显异常。

A strain of bacterial pathogen named as db14 was isolated from a cultured turbot（Scophthalmus maximus） fry with the symptom of subcutaneous hemorrhage around the mouth, and gray and atrophyic liver. Strain db14 grew slowly on the LB medium, and the colonies were caelate, white and hard. The intraperitoneal injection experiment revealed that the strain was virulent to turbot with an LDso value of 2.75 × 10^3 colony forming units/g. The strain was similar in biochemical and biophysical properties to Aeromonas salmonicida subsp, achromogenes. Compared to the similar sequences in the GenBank database, the sequence of 16S rDNA of strain db14 shared a high similarity to that of A. salmonicida subsp, achromogenes. Based on the results obtained, strain db14 was identified as A. salmonicida subsp, achromogenes. The chemotherapeutant sensitivity test showed that fortum, chloramphenicol, ceftriaxone and amikacin could effectively inhibit the growth of the strain db14. When challenged by strain db14, there were obvious pathological changes in the turbot tissue of liver, kidney, spleen and intestine in the pathological sections of the fish, and the tissues of the heart and brain looked normal.