怀头鲇体表溃烂症病原鉴定及致病性分析

Identification of the causative pathogen causing skin-ulcer in Silurus soldatovi and its pathogenicity

为探讨黑龙江流域怀头鲇体表溃烂症的病因及防控措施,本研究采用常规方法从患病鱼的肝脏、脾脏和肾脏等部位分离病原菌,通过人工感染试验确定分离菌株的致病性,并对菌株的基本形态、理化特性、分子特征、毒力基因携带情况及耐药性等进行了系统研究。结果显示,从患病鱼体内分离得到3株病原菌,分别命名为NY-8、NY-9和NY-12;人工感染试验发现,NY-8和NY-9株对试验鱼有较强的致病力,NY-12株毒力较弱;3株细菌混合感染后,鱼体发病症状与临床自然发病症状一致,试验鱼死亡率高达到100%。综合理化特征和16S r RNA基因序列分析结果,确定NY-8、NY-9和NY-12株分别为气单胞菌属的维氏气单胞菌、杀鲑气单胞菌和嗜水气单胞菌。5种毒力基因在3株气单胞菌中的分布表现为两种基因型,h l y+/a e r+/a c t+/a l t+/G C A T+和h l y+/a e r-/act+/alt+/GCAT+,同时携带5种毒力基因的NY-8和NY-9分离株致病性显著高于NY-12株。3株细菌在耐药谱上有一定差异性,NY-8和NY-9株均对4种氟喹诺酮类药物敏感,对氨基糖苷类、呋喃类等药物耐药;NY-12株仅对左氧氟沙星和氟苯尼考等2种药物敏感。

In order to investigate the cause and prevention measure of skin-ulcer of Silurus soldatovi in Heilongjiang River,the pathogenic bacteria were isolated from the liver,spleen and kidney of diseased S.soldatovi with conventional methods.Artificial infection experiment was carried out to prove the pathogenicity of isolated strains.The morphological,biochemical,molecular and characteristics,virulence genes and antimicrobial resistance to bacteria were examined.The results indicated that 3 pathogenic strains were isolated from diseased fish,named NY-8,NY-9 and NY-12,respectively.Artificial infection showed that NY-8 and NY-9 were highly pathogenic to experimental fish while NY-12 strain was less virulent to fish.Co-infection of 3 strains caused 100%mortality of fish with the same clinical signs as the natural case.Combining the biochemical and molecular characteristics of 3 strains,NY-8,NY-9 and NY-12 were determined to be Aeromonas veronii,A.salmonicida and A.hydrophila,respectively.The three strains contained two virulence genotypes,including hly+/aer+/act+/alt+/GCAT+and hly+/aer-/act+/alt+/GCAT+.The pathogenicity of NY-8 and NY-9 carrying all five virulence genes was significantly higher than that of NY-12.Antimicrobial susceptibility tests showed that there were some differences in drug resistance spectrum in 3 strains.NY-8 and NY-9 were sensitive to 4 kinds of fluoroquinolones and resistant to aminoglycoside and nitrofurans antibiotics,while NY-12 was only sensitive to levofloxacin and florfenicol.