In 2017, Siberian sturgeon (Acipenser baerii) were found a massive death in a sturgeon culture farm in Fukang City, Xinjiang, and had clinical symptom of haemorrhage in red and swollen anus and punctate hemorrhage in abdomen.A dominant bacterium named XB2was isolated from the liver and spleen of the diseased Siberian sturgeon, and identified through gram stain, physiology, biochemistry, and 16S rRNA gene sequences analysis by Mega 6.0.The results showed that XB2was a gram-negative brevibacterium, either alone or in pairs, V-P reaction positive, and used sucrose, fructose, glucose, gelatin, and citric acid, with production of acid in stead of gas.XB2grew in 1％ (m/V) sodium chloride and did not grow in more than 3％ (m/V) sodium chloride, with growth at 20—30℃and without growth at 4°C and 37°C.XB2did not utilize lactose, salicin, cellobiose, hydrogen sulfide, tartaric acid and arabinose.Phylogenetic tree indicated that XB 2had homology of 99％with Yersinia ruckeri (KJ812974), with LD50of 2.37×104cfu/mL.The drug sensitivity test showed that XB 2is sensitive to Florfenicol, Levofloxacin, Piperacillin and Azlocillin, and resistant to Midecamycin, Spectinomycin, Streptomycin and Ampicillin.%2017年, 新疆阜康市某鲟鱼养殖场的西伯利亚鲟出现大批死亡, 主要症状为生殖孔红肿外突, 腹部有点状出血.自患病西伯利亚鲟肝脏、脾脏分离到一株优势菌株XB2, 通过革兰氏染色、生理生化试验、药敏试验, 并对其16SrRNA基因序列进行测定, 用Mega 6.0对序列进行分析.生理生化试验结果显示, 菌株XB2为革兰氏阴性短杆菌, 单独或成对出现;产酸不产气, V-P反应呈阳性, 能利用蔗糖、果糖、葡萄糖、明胶、枸橼酸;在含1％ (m/V) 氯化钠中能生长, 高于3％ (m/V) 氯化钠中不生长;在4℃不生长, 20～30℃均能生长, 但在37℃不生长;不利用乳糖、水杨苷、纤维二糖、硫化氢、酒石酸、阿拉伯糖.进化树显示, 菌株XB2与鲁氏耶尔森菌KJ812974同源性达99％.通过回感试验确定其半致死密度为2.37×104 cfu/mL.结合生理生化鉴定结果和16SrRNA基因序列分析结果, 确定菌株XB2为鲁氏耶尔森菌.药敏结果显示, 鲁氏耶尔森菌XB2对氟苯尼考、左氧氟沙星、哌拉西林、阿洛西林等9种药物敏感, 对麦迪霉素、大观霉素、链霉素、氨苄西林等15种药物耐药.
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