虾夷扇贝育苗阶段幼体细菌性病原的确定

本研究确定了獐子岛集团虾夷扇贝Patinopecten yessoensis育苗过程中幼体大规模死亡的病原菌。采用TCBS培养基从患病幼体中分离弧菌,其数量为1.12×10⁴ CFU/g,以V1菌株和V2菌株为优势菌,占总弧菌数的64.3%和32.1%。用血琼脂平板测定V1菌株和V2菌株的溶血性,2株菌分别呈β溶血和α溶血。用2株菌分别感染扇贝幼体,幼体的死亡率显著高于对照组(P<0.05),症状与自然状态下的发病症状一致,并且从感染死亡的幼体中分离到原感染菌株,确定V1菌株和V2菌株是造成扇贝幼体大规模死亡的病原菌。对2株病原菌进行致病基因分析,结果发现V1菌株含有胞外金属蛋白酶基因。经16S rRNA基因测序分析,V1菌株(GenBank登录号KR232924)和V2菌株(GenBank登录号KR232925)与Vibrio splendidus ctt 31/5 和 Vibrio tasmaniensis 007的相似度分别为99.9%和99.2%。用药敏纸片扩散法检测病原菌对常见抗生素的敏感性,结果表明利福平、氟苯尼考和磺胺异恶唑均能有效抑制病原菌的生长。

Identification of bacterial infections associated with larval development of Yesso scallop

The pathogens causing mortality in Yesso scallop (Patinopecten yessoensisis) larvae in the hatchery of Zhangzidao Group Co. Ltd. were identified. A high mortality of the Yesso scallop larvae occurred during the seedling process: the larvae lost their ability to swim, their cilia fell off and their valves closed, they then sank to the bottom of the nursery pond and died. Vibrio has been reported as the primary pathogen for massive mortalities of different bivalves both in hatchery and in the field worldwide. Total viable vibrios counts in moribund larvae were 1.12×10⁴ CFU/g on Tryptone Citrate Bile Sucrose agar plates. Two dominant strains, named V1 and V2, accounted for 64.3% and 32.1% of total vibrios counts respectively. Blood agar plates were used to measure hemolysis of isolated strains. Strain V1 exhibited beta hemolysis, while strain V2 exhibited alpha hemolysis. A challenge test showed that the signs of infected larvae were identical to those of natural moribund larvae, the cumulative mortality caused by strains V1 and V2 was significantly higher than that of the control (P<0.05) and bacteria were re-isolated from the dead larvae. Strains V1 (GenBank Accession No: KR232924) and V2 (GenBank Accession No: KF232925) shared 99.9% and 99.2% identity with Vibrio splendidus ctt 31/5 and Vibrio tasmaniensis 007, respectively, by 16S rDNA sequencing. The presence of genes coding for virulence factors was examined by PCR analysis, showing that strain V1 possessed the extracellular metalloprotease (vsm) gene. Antibiotic susceptibility assays showed that both strains were sensitive to the rifampicin, florfenicol and sulfafurazole.