Terceti Mateus S, Ogut Hamdi, Osorio Carlos R
Instituto de Acuicultura, Universidade de Santiago de Compostela, Santiago de Compostela, Galicia, Spain.
Bursa Technical University, Faculty of Natural Sciences, Architecture and Engineering, Department of Bioengineering, Bursa, Turkey.
Appl Environ Microbiol. 2016 Jun 13;82(13):3736-3745. doi: 10.1128/AEM.00781-16. Print 2016 Jul 1.
Photobacterium damselae subsp. damselae is considered to be an emerging pathogen of marine fish of importance in aquaculture, with a notable increase in its geographical distribution during the last several years. In this study, we carried out for the first time to our knowledge a genetic and pathobiological characterization of 14 strains isolated from sea bass (Dicentrarchus labrax) reared in the Southeastern Black Sea, where high mortalities were observed at two aquaculture farms during the summer and autumn of 2011. Heterogeneity was evidenced among strains in phenotypical traits, such as sucrose fermentation, motility, and hemolysis. Although 11 of 14 isolates were hemolytic, we found that all of the isolates lacked the pPHDD1 virulence plasmid that encodes the phospholipase-D damselysin (Dly) and the pore-forming toxin PhlyP, two hemolysins previously reported to constitute major virulence factors for turbot. Subsequent PCR and sequencing analyses demonstrated that the 11 hemolytic isolates harbored a complete hlyAch gene, a chromosome I-borne gene that encodes HlyAch hemolysin, whereas the three nonhemolytic isolates contained hlyAch pseudogenes caused by insertion sequence elements. Virulence challenges with two representative strains revealed that, albeit less virulent than the pPHDD1-harboring strain RM-71, the plasmidless hlyAch-positive and hlyAch-negative Black Sea isolates were pathogenic for sea bass. A phylogenetic analysis based on the toxR gene sequence uncovered a greater diversity in the isolates, indicating that the presence of this pathogen in the Black Sea was not caused by the introduction and spread of a single virulent clone but by the proliferation of different clones.
The geographical distribution of marine bacterial pathogens is undergoing a worldwide increase. In particular, bacteria of the group vibrios are increasingly being isolated as the causative agents of disease in novel species of cultivated fish in areas where they had not been previously reported. Here we characterize for the first time to our knowledge a collection of isolates of the fish and human pathogen Photobacterium damselae subsp. damselae from diseased sea bass reared in the Black Sea. We uncovered great genetic diversity in the Black Sea isolates of this pathogen, suggesting a multiclonal origin. We also demonstrate for the first time that these isolates bear pathogenic potential for sea bass cultures by virulence challenges.
美人鱼发光杆菌美人鱼亚种被认为是水产养殖中对海洋鱼类具有重要意义的一种新兴病原体，在过去几年中其地理分布显著增加。在本研究中，据我们所知，我们首次对从黑海东南部养殖的海鲈（欧洲鲈）中分离出的14株菌株进行了遗传和病理生物学特征分析，2011年夏秋两季，在两个水产养殖场观察到了高死亡率。菌株在表型特征上存在异质性，如蔗糖发酵、运动性和溶血作用。虽然14株分离株中有11株具有溶血活性，但我们发现所有分离株都缺乏编码磷脂酶D（Dly）和孔形成毒素PhlyP的pPHDD1毒力质粒，这两种溶血素先前被报道是大菱鲆的主要毒力因子。随后的PCR和测序分析表明，11株溶血分离株含有完整的hlyAch基因，这是一个位于染色体I上编码HlyAch溶血素的基因，而3株非溶血分离株含有由插入序列元件导致的hlyAch假基因。用两株代表性菌株进行的毒力挑战试验表明，尽管比携带pPHDD1的菌株RM - 71毒力弱，但无质粒的hlyAch阳性和hlyAch阴性黑海分离株对海鲈具有致病性。基于toxR基因序列的系统发育分析揭示了分离株中存在更大的多样性，表明黑海地区这种病原体的存在不是由单一毒力克隆的引入和传播引起的，而是由不同克隆的增殖导致的。
海洋细菌病原体的地理分布正在全球范围内增加。特别是，弧菌属细菌越来越多地被分离出来，作为以前未报道过的养殖鱼类新物种疾病的病原体。在此，据我们所知，我们首次对来自黑海患病海鲈的鱼类和人类病原体美人鱼发光杆菌美人鱼亚种的分离株进行了特征分析。我们发现该病原体的黑海分离株具有很大的遗传多样性，表明其起源是多克隆的。我们还通过毒力挑战首次证明这些分离株对海鲈养殖具有致病潜力。
