罗非鱼绿色气球菌的鉴定及致病性研究

STUDIES ON IDENTIFICATION AND PATHOGENICITY OF AEROCOCCUS VIRIDANS ISOLATED FROM TILAPIA

研究首次报道了从广东茂名市茂南区患病罗非鱼体内分离的两特殊细菌菌株Mnlv1和Mnlv2,通过细菌形态学、培养条件比较、生理生化特征及16S rRNA基因检测等鉴定了该病原,采用三种不同的感染方式对罗非鱼实施人工感染以期探讨该菌对罗非鱼的致病强度及致病条件,同时也比较了两菌株对29种不同的抗生素的敏感性差异。结果表明:两菌株均为绿色气球菌(Aerococcus viridans),革兰氏染色阳性(G+),α溶血性。感染实验结果显示,该菌株对罗非鱼具有较强的致病性,并且随着环境胁迫作用的加强,鱼体发病死亡率增高。药敏试验结果显示,两菌株为对头孢曲松、米诺四环素、诺氟沙星等15种药物高度敏感,对麦迪霉素、壮观霉素和新霉素3种药物中度敏感,对红霉素、乙酰螺旋霉素、苯唑青霉素等10种药物不敏感。研究将为罗非鱼绿色气球菌病原的诊断及防治提供理论基础。

Tilapia is an important species in freshwater aquaculture and widely cultures in tropical and subtropical regions of many countries.It is famous for rapid growth,well-adapted,fast-breeding and higher disease resistance.Like other large fish,they take a good supply of protein for human and are very popular among artisanal and commercial fisheries.However,with the unscientific husbandry,environmental degradation and other reasons,tilapia is no longer a disease-resistant species.There are a number of bacterial and viral diseases,and many of them are devastating,such as Streptococcus and Edwarsiella tarda.So understanding and identifying the new causative agent of different disease is significant for the future culture of tilapia.In this study,we firstly isolated two Aerococcus spp.Mnlv1 and Mnlv2 from diseased tilapia in Maonan of Guangdong Province.With a series of experiment,such as bacterial morphology,condition comparison of culture,physiological and biochemical property and 16S rRNA gene analysis,the two strains were identified as Aerococcus viridans.Moreover,in order to study the pathogenicity and aetiological condition of this organism,we employed three different artificial pathways to infected tilapia.In addition,twenty-nine antibiotics were selected to test the sensitivity to Aerococcus viridans.The results showed that Aero-coccus viridans was pathogenic to tilapia but it generally could not infect healthy tilapia actively.It likely to be a conditional pathogen and the environmental stress could enhance their infection to tilapia.The drug sensitive detection showed that these two Aerococcus strains were hypersensitive to quinolone group（norfloxacin,Ofloxacin,enrofloxacin,nalidixic acid,Lomefloxacin,enoxacin,Fleroxacin）,part β lactam group（ceftriaxone,cefaclor,Cefazolin,cefobis） and part Aminoglycosides group（Amikacin,Tobramycin,gentamicin） and minocycline,mid-sensitive to midecamycin,Spectinomycin and neomycin,resistant to part macrolides group（erythrocin,acetyl spiramycin,roxithromycin）,part β lactam group（cephalothin,cefalexin,amoxicillin,oxacillin,penicillin,ampicillin） and tetracycline.