锯缘青蟹混合感染症致病菌的分离鉴定与感染治疗

Isolation and identification of two bacterial pathogens from mixed infection mud crab Scylla serrata and drug therapy

从汕头市牛田洋水产养殖区的患病锯缘青蟹Scylla serrata中分离纯化到2株优势细菌,在TCBS培养基上生长,颜色呈黄色的命名为HY,呈绿色的命名为HG,两者都是革兰氏阴性杆菌。人工感染此两株细菌的健康青蟹均产生与自然病蟹相同的症状和组织病理变化,并导致死亡,说明它们都是青蟹的病原菌。以这两种细菌的DNA为模板,采用细菌16S rRNA基因的通用引物进行PCR扩增,测序后分别获得HY的1509bp和HG的1532bp核苷酸序列。通过基因序列同源性比对和系统发育树分析,结合细菌生理生化特性分析,HY和HG分别被鉴定为嗜水气单胞菌Aeromonas hydrophila和副溶血弧菌Vibrio parahaemolyticus。这是首次报道嗜水气单胞菌为青蟹的病原菌。两种病原菌均对阿莫西林、氧氟沙星、庆大霉素、链霉素高度敏感,对磺胺嘧啶、甲砜霉素中度敏感,对青霉素钠不敏感。采用嗜水气单胞菌浸泡感染或注射感染青蟹,发病后进行阿莫西林药浴3天,均获得100%的治疗效果。

Two preponderant bacterial strains were isolated from the infected mud crab（Scylla serrata） in Niutianyang aquaculture area of Shantou.One displayed yellow color and the strain was named as HY,the other showed green color and the strain was named as HG after growing on the TCBS agar plate.Both of them were rod shape and displayed gram negative.After healthy S.serrata individuals were infected with HY or HG by intramuscular injection,obvious histopathological changes could be observed in their tissues as those in the naturally diseased S.serrata,which lead them to their death.These results demonstrate that both HY and HG are pathogens of S.serrata.With the total HY or HG DNA as a template and bacterial 16S rRNA gene universal primers as primers,PCR amplification could obtain a partial HY sequence with 1509bp and HG fragment with 1532bp.Based on the blasting of 16S rRNA gene sequence and phylogenetic tree,together with the physiological and biochemical characteristics analysis,HY and HG were identified as Aeromonas hydrophila and Vibrio parahaemolyticus,respectively.To our knowledge,this is the first report that A.hydrophila is a pathogen of S.serrata.Both HY and HG showed high sensitivity to Ofloxacin,Gentamicin,streptomycin and Amoxicillin,medium sensitivity to Sulfadiazine and Thiamphenicol,and no sensitivity to Benzylpenicillin Sodium.After the healthy mud crabs were infected with A.hydrophila by immersion or intramuscular injection and displayed typical symptoms,drug therapy shows 100% success rate after the infected crabs were bathed in Amoxicillin at 15μg/mL for three days.