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2001年9月—12月,浙江舟山部分网箱养殖红拟石首鱼发生了陆续死鱼,发病鱼表现为眼球突出、浑浊,失去方向性,皮肤溃疡等症状。从病鱼的肾脏和肝脏中分离到菌株SO-2和SO-3,对两分离株进行了致病性试验,发现两者对红拟石首鱼、罗非鱼及小白鼠均有致病力,SO-2和SO-3对红拟石首鱼、罗非鱼及小白鼠的LD50分别为4.8×108CFU/尾和1.9×107CFU/尾2、.8×108CFU/尾和8.3×107CFU/尾及9.6×106CFU/只和4.2×106CFU/只,试验感染鱼出现眼球突出、浑浊及失去方向性等与自然发病相似症状,确定该两株菌为致病菌。两分离株为革兰氏染色阳性,呈链状球菌,β溶血,10℃生长,45℃不生长;接触酶阴性,水解七叶灵、精氨酸;VP试验、脲酶和马脲酸试验阴性,发酵葡萄糖、水杨苷、蔗糖和淀粉,不发醇阿拉伯糖、菊糖、乳糖、蜜二糖、棉子糖和山梨醇。分离株对氨卞青霉素、万古霉素和先锋Ⅴ等高度敏感,对庆大霉素、复方新诺明、林可霉素、氟哌酸等不敏感。应用16SrRNA基因进行的菌株PCR鉴定,确定该两株菌为海豚链球菌。
From September 2001 to December 2001, part of the cages were cultured in Zhoushan, Zhejiang Province. One of the dead fish appeared in the cages of Zhuhai, Zhejiang Province. Occurrences of the diseased fish showed prominent, turbid, unobtrusive and skin ulcers. Strain SO-2 and SO-3 were isolated from the kidney and liver of diseased fish and the pathogenicity test was carried out on the two isolates. The results showed that both of them were pathogenic to red tilapia, tilapia and mice LD50 of 4.8 × 108CFU / tail and 1.9 × 107CFU / tail 2, .8 × 108CFU / tail and 8.3 × 107CFU / tail of SO-2, SO-2 and SO- Tail and 9.6 × 106CFU / only and 4.2 × 106CFU / only, the experimental infected fish showed prominent eyeballs, turbidity and loss of direction similar symptoms and other natural onset, to determine the two strains of pathogens. The two isolates were positive for Gram stain, streptococci, β hemolysis, growth at 10 ° C, no growth at 45 ° C; negative contact enzymes, hydrolyzed sesbanol, arginine; VP test, urease and urea were negative , Fermenting glucose, salicin, sucrose and starch, no alcohol arabinose, inulin, lactose, melibiose, raffinose and sorbitol. The isolates were highly sensitive to ampicillin, vancomycin and vanguard Ⅴ, insensitive to gentamicin, cotrimoxazole, lincomycin and norfloxacin. The 16SrRNA gene was used for PCR identification of the strains, and the two strains were identified as Streptococcus viridans.