罗非鱼无乳链球菌生物学特性与致病力研究

本试验分离纯化1株致使罗非鱼具有链球菌发病症状的病原菌,药敏试验结果表明,该菌对氯霉素等10种药物敏感。PCR扩增该菌的cfb基因,将扩增片段测序后与GenBank上登录的罗非鱼无乳链球菌的cfb基因序列进行比对。同时对该病原菌的生物学特性进行研究,包括培养时间和pH对该菌生长的影响;培养温度对其致病力的影响;探讨了不同攻毒方式(腹腔、胸腔和背部肌肉注射)与鱼发病快慢的关系;并对不同规格(100和10 g左右)的罗非鱼对该菌的易感性进行分析。试验结果表明,该病原菌为无乳链球菌(Streptococcus agalactiae);该菌的最适培养时间为11.5 h,最适培养pH为7.5;腹腔、胸腔和背部肌肉注射后,其发病时间几乎一致,但胸腔注射的试验鱼死亡速度最慢,背部肌肉注射是较安全可行的攻毒方式;33℃培养的无乳链球菌攻毒的罗非鱼发病最快,死亡最集中;100 g的试验鱼比10 g的试验鱼更易感染。

Biological Characteristic and Pathogenicity Research of Streptococcus agalactiae in Tilapia

A strain of bacteria was isolated from the attacked tilapia. The pathogen was studied after isolation and purification. A drug sensitivity test showed that the pathogen was sensitive to 10 drugs containing chloramphenicol.The cfb gene was cloned and sequenced.The biological characteristics of the pathogen were studied.The test included many aspects, such as effect of cultivating time and pH on the growth, effect of cultivating temperature on the virulent,the relationships between disease outbreak rate and attacking manners, susceptibility of different specifications(100 and 10 g)fish to the bacteria. The results indicated that the pathogen was Streptococcus agalactiae of tilapia, and the best time and pH for cultivating was 11.5 h and 7.5, respectively. The onset of three injection methods (peritoneal, pleural and back muscle) was the same, but the slowest death rate was the one injected by pleural. Back muscle injection was safer to youngfish. The fish was attacked fastest and had the most centralized death rate when cultivating temperature was 33℃. The 100 g fish was easier to be attacked than the 10 g fish.