Isolation,identification and grow th of pathogenic bacterium in enteric redmouth disease in rainbow trout Oncorhynchusmykiss
LIAN Hao-miao1,2,LU Tong-yan1,LIU Hong-bai1,YIN Jia-sheng1,ZHANG Hui2,LIShao-wu1,
1.Heilongjiang River Fisheries Research Institute,Chinese Academy of Fishery Sciences,Harbin 150070,China;2.College of Animal Science and Technology,Northeast Agricultural University,Harbin 150030,China
Abstract: A bacterial strain BH1206 was isolated from liver and spleen of rainbow trout Oncorhynchusmykiss diseased with enteric redmouth,and identified by artificial infection test,by a conventional biochemicalmethod,by an API 20E kit,by a Biolog identification system,and by amolecular sequencingmethod.The fish infected with BH1206 had clinical signs including punctuate haemorrhaging on the body surface,especially on the abdominal wall and rostral side.Different degree of hemorrhageswere observed in all visceral organs.Itwas found that the isolated strain was a Gram-negative bacterium,oxidase-negative aerobic non-fermented Bacillus.The physical and chemical characteristics and Biolog system analysis revealed that BH1206 was identified as Yersinia ruckeri.In the phylogenetic tree constructed by comparing the 16S rRNA sequence of the strain BH1206(GenBank accession number KJ850444)with other relative bacterial species in the GenBank,BH1206 and Yersinia ruckeri were clustered in a branch.The optimum growth of BH1206 was found under condition of pH 6.5-7.5,a salinity of0,and temperature 28-30℃.Antimicrobial susceptibility tests showed that BH1206 was highly susceptible to 11 kinds of drugs including ofloxacin,ciprofloxacin,norfloxacin,enrofloxacin,levofloxacin,chloramphenicol,tetracycline, doxycycline,tetracycline,and trimethoprim-sulfamethoxazole carbenicillin,while completely resistant to amoxicillin,rifampin,and polymyxin.The findings indicate that Yersinia ruckeri is the pathogen for enteric redmouth of rainbow trout and provide a reference for the disease prevention.
2015, Vol. 30 
