湖北吉富罗非鱼源Ⅰa无乳链球菌毒力分析及药敏特性

Virulence analysis and drug sensitivity of type Ia Streptococcus agalactiae isolated from the genetic improvement of farmed tilapia in Hubei

为探明湖北荆州某养殖场吉富罗非鱼(Genetic Improvement of Farmed Tilapia,GIFT)致病原因,对感染的罗非鱼精准施治,本研究从湖北荆州某养殖场患病吉富罗非鱼脑组织分离到一株优势菌。结果显示:该菌在BHI平板上生长出光滑、圆形、白色菌落,显微镜观察发现细菌呈单个、成对或球形短链状,长短不一,且革兰氏染色为阳性。经16S rRNA序列、PCR鉴定和生理生化特性鉴定,确定分离菌株为罗非鱼无乳链球菌,命名为JZ-202108。分离菌株JZ-202108血清型为Ⅰa型,携带gapC、sodA、bac、bca和hly等5种毒力基因。分离菌株JZ-202108人工感染吉富罗非鱼的症状与自然发病症状类似,出现神经症状和严重的内脏出血现象,并从脑组织中分离到强毒株,其LD_(50)为3.4×10^(5)CFU/尾,对吉富罗非鱼致病性较强。药物敏感性实验表明,分离菌株JZ-202108对β-内酰胺类、头孢类药物敏感,对氨基酸糖苷类药物耐药;乌梅、黄连、朱砂、野菊花等中药对JZ-202108菌株有明显抑制作用,乌梅和野菊花在菌株JZ-202108感染吉富罗非鱼的体内治疗效果最佳。生产中可考虑用β-内酰胺和头孢类抗菌药物,以及中药乌梅和野菊花等药物进行治疗。

A dominant strain of bacteria was isolated from the brain tissue of diseased GIFT from the farm to investigate the cause of genetic improvement of farmed tilapia(GIFT)on a farm in Jingzhou,Hubei,and to treat the infected tilapia precisely.The results showed that the bacteria grew smooth,round,white colonies on BHI plates,and microscopic observation revealed that the bacteria were single,paired or spherical in short chains of varying lengths and positive for Gram staining.The isolated strain was identified as Streptococcus agalactiae by 16S rRNA sequence,PCR,and physiological and biochemical characteristics and was named JZ-202108.The isolate JZ-202108 was serotype Ia and carries five virulence genes,such as gap C,sod A,bac,bca and hly.The symptoms of artificial infection of JZ-202108 were similar to those of natural disease,with neurological symptoms and severe visceral hemorrhage,and a robust virulent strain was isolated from brain tissue of the diseased GIFT with an LD_(50)of 3.4×10^(5)CFU/tail,which was highly pathogenic to GIFT.The drug sensitivity test showed that the isolated strain JZ-202108 was sensitive toβ-lactams and cephalosporins and resistant to amino acid glycoside drugs.Chinese herbal medicines such as Mume,Coptis Chinensis,Cinnabar and Wild Chrysanthemum had significant inhibitory effects on strain JZ-202108,and Mume and Wild Chrysanthemum had the best therapeutic effect in the JZ-202108 infected tilapia in vivo.In production,β-lactam and cephalosporin antibiotics,as well as Chinese medicine Fructus Mume and Mother chrysanthemum,can be considered for treatment for S.agalactiae infection.