2株亚东鲑源气单胞菌的鉴定及其致病性与药敏特性分析

亚东鲑(Salmo trutta fario)是西藏地区重要的冷水性经济鱼类之一。为明确亚东鲑暴发性死亡的原因, 对从患病亚东鲑体内分离得到的 2 株优势细菌 B1、A3-2 进行种类鉴定、毒力基因检测、动物回归感染、耐药基因检测和药敏试验。结果显示, 2 株优势细菌鉴定为杀鲑气单胞菌(Aeromonas salmonicida) B1 和温和气单胞菌(Aeromonas sobria) A3-2。杀鲑气单胞菌 B1 对亚东鲑具有较强的致病性, 而温和气单胞菌 A3-2 对亚东鲑未表现出致病性。杀鲑气单胞菌 B1 携带有 10 种毒力基因: 外毒素(AerA、Act 和 hly 基因)、胞外酶(gcat、ahyB 和 Lip 基因)、Ⅲ型分泌系统(aexT、aopP 和 ascF-G 基因)、鞭毛(Fla 基因); 温和气单胞菌 A3-2 携带有 5 种毒力基因: 外毒素(Act 和 Alt 基因)、胞外酶(gcat 基因)、Ⅲ型分泌系统(aexT 和 aopP 基因)。杀鲑气单胞菌 B1 对头孢曲松、阿莫西林、氟苯尼考、环丙沙星、四环素、链霉素等 21 种抗菌药物敏感, 仅对万古霉素耐药; 温和气单胞菌 A3-2 对头孢曲松、氟苯尼考、环丙沙星、吡哌酸、四环素、链霉素等 17 种抗菌药物敏感, 对青霉素、阿莫西林、磺胺异噁唑、复方新诺明、万古霉素等 6 种药物耐药。杀鲑气单胞菌 B1 含有 AmpC、gyrA 和 parC 等 3 种耐药基因; 温和气单胞菌 A3-2 含有 AmpC、gyrA、parC 和 tetE 等 4 种耐药基因, 2 种气单胞菌的耐药基因检出结果与耐药表型基本一致。杀鲑气单胞菌 B1 是引起亚东鲑暴发性死亡的重要病原菌, 本研究为亚东鲑养殖过程中杀鲑气单胞菌的感染特征、疫苗研制和疾病防控提供了基础数据。

Identification of two Aeromonas strains from Salmo trutta fario and analysis of their pathogenicity and drug sensitivity characteristics

Salmo trutta fario is one of the important cold-water economic fishes in Tibet. S. t. fario is delicious; contains no muscle spines; and is rich in amino acids, unsaturated fatty acids, and vitamins. It has become an important local high value-added aquaculture species. Diseases occur frequently in cultured S. t. fario,especially bacterial diseases such as gill rot and furuncle disease and fungal diseases such as saprolegniasis, which has caused huge economic losses to the S. t. fario farming industry. Therefore, disease research is of great significance to the large-scale healthy culture of S. t. fario. To determine the cause of death of S. t. fario, two dominant strains B1 and A3-2 were isolated from diseased S. t. fario and analyzed for virulence gene, animal regression infection, drug resistance gene, and drug sensitivity. The two dominant strains were identified as Aeromonas salmonicida B1 and Aeromonas sobria A3-2. A. salmonicida B1 showed strong pathogenicity to S. t. fario,while A. sobria A3-2 showed no pathogenicity to S. t. fario. Ten virulence genes were detected in A. salmonicida B1, including those of exotoxin (AerA, Act, and hly genes), extracellular enzyme (gcat, ahyB, and Lip genes), secretion system of III type (aexT, aopP, and ascF-G genes), and flagella (Fla gene). Five virulence genes were detected in A. sobria A3-2, including those of exotoxin (Act and Alt genes), exoenzyme (gcat genes), and secretory system III (aexT and aopP genes).A. salmonicida B1 was sensitive to 21 antibiotics, such as ceftriaxone, amoxicillin, florfenicol, ciprofloxacin, tetracycline, and streptomycin, and was only resistant to vancomycin. A. sobria A3-2 was sensitive to 17 antimicrobial drugs, such as ceftriaxone, florfenicol, ciprofloxacin, pipemidic acid, tetracycline, and streptomycin and was resistant to 6 antibiotics, including penicillin, amoxicillin, sulfisoxazole, trimethoprimsulbactam, and vancomycin. Three types of drug-resistant genes (AmpC, gyrA, and parC) were detected in A. salmonicida B1. Four types of drug-resistant genes (AmpC, gyrA, parC, and tetE) were detected in A. sobria A3-2. The drug-resistant genes detected in the two Aeromonas strains were basically consistent with the drug-resistant phenotype. A. salmonicida B1 was found to be an important pathogen causing fulminant death in S. t. fario. This study provides fundamental data on the infection characteristics of A. salmonicida, for vaccine development and disease prevention and control in the breeding process of S. t. fario.