草鱼暴发性出血病病原分离、毒力基因检测与药敏分析

The virulence characteristics and drug susceptibility of outbreak hemorrhage disease pathogen isolated from grass carp Ctenopharyngodon idllus

从草鱼体内分离到致病菌株Jxsks1,该菌株对草鱼的LD50值为2.3×103CFU/g鱼体质量,为强致病菌;经生理生化、16S r DNA和gyr B基因序列测序鉴定为嗜水气单胞菌。ERIC-PCR分型结果表明,该菌株为迄今未见报道的类型。选取丝氨酸蛋白酶ahp、热稳定性肠毒素ast、气溶素aer A、热不稳定性肠毒素alt、鞭毛基因fla、脂酶lip等6种毒力基因特异性引物对该菌株进行PCR检测,结果表明其毒力基因型为aer A^+、alt^+、ast^+、ahp^+、lip^+、fla^-。选取28种抗生素进行药敏检测结果表明,该菌株对喹诺酮类、氨基糖苷类、四环素类、氯霉素、第二代和第三代头孢类等药物敏感,对硝基呋喃类、大环内酯类、多肽类中度敏感,对第一代头孢类、青霉素类、复方新诺明和洁霉素耐药。

A strong pathogenic bacterial strain Jxsks1 was isolated from grass carp,Ctenopharyngodon idllus.The pathogen was identified as Aeromonas hydrophila based on the physiological and biochemical analysis and the sequencing of housekeeping gene 16 S r DNA and gyr B. The LD50 of the bacteria infecting the grass carp via intraperitoneal injection was 2. 3 × 10^3 CFU/g. The results of genetic typing by ERIC-PCR（ enterobacterial repetitive intergenic consensus PCR）-fingerprinting showed that it was a type of A.hydrophila which has not been reported before. The distribution patterns of six virulence genes,including aerolysin（ aer A）,heat-labile cytotonic enterotoxin（ alt）,heat-stable cytotoxic enterotoxin（ ast）,elastase（ ahp B）,lipase（ lip） and flagella（ fla）,were tested by PCR method and the results showed that its virulence-gene pattern was aer A＋,alt＋,ast＋,ahp＋,lip＋,fla-. The drug susceptibility test of 28 antibiotics by paper extension method showed that the strain was susceptible to quinolones, aminoglycoside,tetracyclines,chloramphenicol,the second and the third generation cephalosporins,intermediately sensitive to nitrofurans,macrolides and polypeptides,but resistant to the first generation cephalosporins,penicillins,sulfamethoxazole compound and lincomycin.