Meyer Gary R, Lowe Geoffrey J, Gilmore Scott R, Bower Susan M
Fisheries and Oceans Canada, Pacific Biological Station, Nanaimo, BC V9T 6N7, Canada.
Dis Aquat Organ. 2017 Jun 19;125(1):79-84. doi: 10.3354/dao03130.
During the fall of 2015, up to 40% mortality occurred in juvenile Yesso scallops Patinopecten yessoensis at an aquaculture site in Baynes Sound, British Columbia, Canada. Macroscopic lesions were present in 11% of the scallops, and histopathology consisting of multifocal and diffuse haemocyte infiltration was observed in 44% of the specimens examined. Histologically, small Gram-negative intracellular bacteria-like particles were observed within necrotic haemocytes of the lesions, suggesting a bacterial aetiology. DNA was extracted from adductor muscle lesions of diseased scallops, and the 16s rDNA gene as well as the DNA-directed RNA polymerase beta subunit (rpoB) were amplified by PCR. Sequence analyses of the resulting 413 and 925 bp fragments were a 100% match to the reference sequence for Francisella halioticida, originally described as the cause of mortality in abalone from Japan. Isolation and culture of the bacteria was not possible at the time, as no further diseased specimens were available. Results from in situ hybridization assays as well as examination by transmission electron microscopy provide further evidence supporting the hypothesis that F. halioticida was the most probable causative agent of the lesions and mortality.
2015年秋季，加拿大不列颠哥伦比亚省贝恩斯湾一个水产养殖场地的虾夷扇贝稚贝死亡率高达40%。11%的扇贝出现肉眼可见的病变，在44%的检查样本中观察到组织病理学变化，表现为多灶性和弥漫性血细胞浸润。组织学检查发现，病变坏死血细胞内有革兰氏阴性、类似细胞内细菌的小颗粒，提示病因是细菌。从患病扇贝的闭壳肌病变中提取DNA，通过聚合酶链反应（PCR）扩增16s rDNA基因以及DNA依赖性RNA聚合酶β亚基（rpoB）。对得到的413和925 bp片段进行序列分析，结果与最初被描述为导致日本鲍鱼死亡原因的哈氏弗朗西斯菌（Francisella halioticida）参考序列100%匹配。当时无法进行细菌的分离和培养，因为没有更多患病样本。原位杂交试验结果以及透射电子显微镜检查提供了进一步证据，支持哈氏弗朗西斯菌是病变和死亡最可能病因的假说。
