一株从草鱼中分离的嗜水气单胞菌的病原学及基因组特征

Etiology and genomic characteristics of an Aeromonas hydrophila strain isolated from Ctenopharyngodon idella

为确定南昌地区某渔场草鱼出血性败血症的病原体及病原特征,从患病草鱼的肝脏病灶中分离出一株致病菌A1310。对分离菌进行了形态特征、理化特性等表型生物学检验、人工感染实验及对抗菌药物的敏感性实验,并对其进行了全基因组测序、基于多序列位点分型(multilocus sequence typing,MLST)的系统进化分析及毒力基因分析。结果显示,生理生化鉴定证明该菌为嗜水气单胞菌,当浓度达1.0×10~6 CFU/mL时,对草鱼有致病性;对供试20种抗菌药物中的青霉素等7种耐药,对卡那霉素等5种敏感;A1310株基因组框架序列共包含96个与毒力和防御相关基因,其中多药耐药性外排泵基因占大多数,约为22%;与美国斑点叉尾鮰分离株(S15-242、S15-458、S15-591、S15-700)聚类为同一进化分支;比较基因组分析发现,A1310具有一个删减版的Ⅵ型分泌系统(typeⅥsecretion system,T6SS),基因数量为标准Ⅵ型分泌系统的80%,缺少vgr G和vca0109基因的部分片段。综上所述,来源于草鱼的嗜水气单胞菌菌株A1310,与美国斑点叉尾鮰分离株具有亲缘关系,含有多个已报道的嗜水气单胞菌的毒力基因。本研究不仅丰富了嗜水气单胞菌的生物学性状内容,也为嗜水气单胞菌的有效检验、防治和深入研究提供一定的参考,对草鱼的疾病防控具有一定意义。

In order to determine the pathogen and pathogenic characteristics of Ctenopharyngodon idella haemorrhagic septicemia in a farm of Nanchang,a strain of pathogenic bacteria A1310 was isolated from the liver lesions of the diseased C.idella.The phenotypic characteristics of the isolated strain A1310 included the morphological characteristics,physiological and biochemical characteristics,pathogenicity,susceptibility test.In addition,the whole genome sequencing,phylogeny-based on multilocus sequence typing(MLST)and virulence gene were examined.According to morphological,biochemical characteristics,the pathogen was identified as Aeromonas hydrophilia.Artificial infection experiments showed that it is pathogenic to C.idella after being infected with the 1.0×10^6 CFU/mL bacteria strains culture.Antibiotic sensitivity test using 20 antimicrobial agents showed that the isolate was resistant to 7 antibiotics including penicillin,but was sensitive to 5 antibiotics including Kanamycin.The A1310 strain genome sequence contains a total of 96 genes related to toxicity and defense,and most of them are multidrug resistance efflux pump genes,about 22%.MLST typing showed that this isolate was genetically related to the American channel catfish isolates(S15-242,S15-458,S15-591,S15-700).Moreover,the comparative genomic analysis showed that A1310 has at least 80%of the core proteins necessary for a complete T6SS,lacking a segment of vgrG and a segment of vca0109.In conclusion,A.hydrophila A1310 from C.idella was genetically related to the American channel catfish isolates genetically and contains multiple reported virulence genes of A.hydrophilia.This study broadened our knowledge to understand the biological traits of A.hydrophlia.This can provide some reference for the effective inspection,prevention,and in-depth study of A.hydrophilia,and it has some significance for the prevention and control of C.idella disease and will be a basis for the disease control during C.idella culture.