杂交鲟出血病病原的分离鉴定与组织病理学观察

为确定重庆彭水地区杂交鲟患病死亡的原因,从患病鲟肝中分离到一株优势菌CQST-2,对其进行形态学观察、人工感染、理化特性测定、分子生物学鉴定、毒力基因检测与药敏试验,进一步对患病组织进行病理观察。结果表明,该菌为革兰氏阴性短杆菌,感染健康杂交鲟可复现与自然患病鱼类似病症;16S rRNA、gyrB、rpoB和cpn60基因与维氏气单胞菌的同源性分别达99.7%、99.9%、99.4%和99.8%,构建的系统发育树与维氏气单胞菌聚为一支;在水温为(22±1)℃时,对杂交鲟的半数致死量LD₅₀为2.0×10⁵ CFU·g^-1;毒力基因检测发现,该菌携带ompA、act、aer、hlyA和alt等5种基因;病理组织观察发现,患病鱼肝细胞结构模糊,肝血窦扩张充血,肠绒毛坏死脱落,肌肉层充血,鳃小片弯曲,上皮细胞增生。药敏试验表明,菌株CQST-2对氧氟沙星、氟苯尼考等18种药物高度敏感,对麦迪霉素、吉他霉素、青霉素等9种抗菌药物耐药。研究结果表明,菌株CQST-2是杂交鲟的致病菌,该菌对杂交鲟具有较强的致病性,可引起多个器官发生病变。

Identification and pathological observation of Aeromonas veronii from hybrid sturgeon (Acipenser baerii♀×Acipenser schrenckii♂)

In order to find out the reason that caused death of hybrid sturgeon in Pengshui, Chongqing, a dominant strain named CQST-2 was obtained from liver of diseased hybrid sturgeon. Pathogen morphological observation, challenge test, physical and chemical characteristics of isolated bacteria, sequence analysis of 16S rRNA,gyrB, rpoB and cpn60 genes, drug test and pathological were carried out and investigated. The result indicated that the isolated strain was a gram-negative bacterium and challenge test symptoms infected with Aeromonas veronii were similar to the natural symptoms. Phylogenetic trees constructed by 16S rRNA, gyrB, rpoB and cpn60 gene sequences were the same as A. veronii, with similarity of 99.7%, 99.9%, 99.4% and 99.8%. The challenge test showed that the value of LD₅₀ was 2.0×10⁵ CFU·g^-1 fish weight by intraperitoneal injection at (22±1)℃. Five virulent genes, including ompA, act, aer, hlyA and alt genes were screened by PCR assay. Pathological observation showed that the structure of liver cells was fuzzy, hepatic sinuses were dilated and congested. Most of intestinal villi were necrotic and exfoliated, and muscle layer was congested.Gills of infected fish were curved and epithelial cells were hyperplasia. Antibiotic resistances showed that the strain was sensitive to 18 drugs, including ofloxacin, polymyxinB, ciprofloxacin, enrofloxacin, and resistance to 9 drugs, including medications, guitamycin, penicillin, et al.This study provided that disease of hybrid sturgeon caused by A. veronii, which had strong pathogenicity and could cause multiple tissue lesions of hybrid sturgeon.