草鱼源致病性维氏气单胞菌的分离鉴定及药物敏感性分析

从贵州兴义某水库网箱养殖的患病草鱼(Ctenopharyngodon idellus)肝脏中分离出菌落大小、形态一致的细菌,编号为GZ09007。经革兰氏染色、生理生化反应等表型鉴定为气单胞菌(Aeromonas)。通过扩增16S rRNA和gyrB基因序列并构建系统发育树,进一步鉴定该菌为维氏气单胞菌(Aeromonas veronii)。该菌株具有act、aer、lip、exu、fla、ser等毒力相关基因,不具有alt、ast、gca T和ahy B等毒力相关基因。人工感染试验表明该菌对草鱼、鲫、团头鲂和鳙均具有强致病性,半数致死量LD_(50)分别为7.45×10~5、1.27×10~5、1.76×10~5和5.36×10~4 CFU·(g·B·W)~(-1)。药物敏感性试验表明该菌对萘啶酸、恩诺沙星和左旋氧氟沙星等12种药物敏感,对新霉素、呋喃唑酮中度敏感,对氨苄西林耐受。研究结果表明维氏气单胞菌GZ09007是引起此次草鱼发病的致病菌。

Isolation, identification and antimicrobial susceptibility of pathogenic Aeromonas veronii isolated from grass carp

A bacterial strain GZ09007 was isolated from the liver of diseased grass carp captured from a reservoir cage in Xingyi city of Guizhou provinceProvince. Gram-staining, physiological and biochemical identification of the bacterium were carried out, and the bacterium was primarily identified as Aeromonas. The phylogenetic trees were constructed by comparing the 16S rRNA and gyrB gene sequence of the isolate with other relative bacteria species in the GenBank databases. The isolate GZ09007 was eventually identified as Aeromonas veronii. It contained act, aer, lip, exu, fla and ser, but did not contain alt, ast, gcaT and ahyB. The artificial infection test showed that the bacterium was highly pathogenic to grass carp, crucian carp, bluntnose black bream and bighead carp and the median lethal dose (LD₅₀) was 7.45×10⁵, 1.27×10⁵, 1.76×10⁵ and 5.36×10⁴ CFU·(g·B·W)^-1, respectively. The antimicrobial susceptibility test showed that the strain was highly sensitive to 12 drugs, such as Nnalidixic, Enrofloxacineenrofloxacine, and Levofloxacin levofloxacin acid etc., intermediately sensitive to Neomycin neomycin and Furazolidonefurazolidone, and resistant to Ampicillinampicillin. The results showed that GZ09007 was the pathogenic bacterium that caused the disease of grass carp.