Park Jiyeon, Roh HyeongJin, Lee Yoonhang, Lee Ju-Yeop, Kang Hyo-Young, Seong Min Ji, Kang Yura, Heo Young Ung, Kim Bo Seong, Park Chan-Il, Kim Do-Hyung
Department of Aquatic Life Medicine, College of Fisheries Science, Pukyong National University, Busan 48513, Republic of Korea.
Department of Aquatic Life Medicine, College of Ocean Science and Technology, Kunsan National University, Gunsan 54150, Republic of Korea.
Microorganisms. 2023 Oct 12;11(10):2546. doi: 10.3390/microorganisms11102546.
is the causative agent of bacterial cold-water disease in salmonids and rainbow trout fry syndrome. This pathogen has attained a global presence and can spread both horizontally and vertically. However, it was not documented in Korea before September 2018. In this study, the objectives were to characterize strain FPRT1, isolated from diseased rainbow trout genotypically and phenotypically. We also conducted various investigations to better understand its impact and assess potential control measures. We acquired fifty rainbow trout (approximately 70 g in weight) and transferred them to a laboratory aquarium. During the initial acclimation period, we observed mortality and examined affected fish for clinical signs. We isolated the bacterium from the spleen of infected rainbow trout using tryptone yeast extract salts agar supplemented with glucose, naming this FPRT1. Antibiotic susceptibility testing was carried out, and from the result, we selected enrofloxacin to administer to the trout orally to reduce mortality. To evaluate pathogenicity, we exposed the trout to FPRT1 at different water temperatures (8, 15, and 22 °C). Genomic analysis was conducted to identify the serotype and relatedness of FPRT1 to European strains. Affected fish displayed clinical signs, such as ulcerative lesions in the mandible, anemia with pale gills, exophthalmia, and increased mucus secretion. Internal symptoms included pale liver and enlarged spleen. FPRT1 was susceptible to erythromycin, enrofloxacin, florfenicol, oxytetracycline, and gentamicin, but resistant to oxolinic acid and sulfamethoxazole/trimethoprim. Oral administration of enrofloxacin resulted in a decrease in mortality from 28% to 6%. Pathogenicity tests revealed varying mortality rates due to FPRT1 at different temperatures. The highest rates were observed at 8 °C (ranging from 43% to 100%) for both intraperitoneal and intramuscular injections, and lower rates occurred at 22 °C (ranging from 0% to 30%), with intramuscular injections displaying higher susceptibility. Genomic analysis identified FPRT1 as serotype 2 and indicated its close genetic relationship with European strains based on the core genome and dispensable genome. The substantial genomic similarity between our strain and European strains suggests the possibility of bacterial spread through the importation of fertilized eggs from Europe. In conclusion, this study highlights the introduction of the previously undocumented pathogen () into Korean rainbow trout populations. The detection of this pathogen and its pathogenicity assessment is not only important for understanding its impact on local aquaculture but also for establishing surveillance and control measures to prevent further transmission and outbreaks in the region.
是鲑科鱼类细菌性冷水病和虹鳟鱼苗综合征的病原体。这种病原体已在全球范围内存在，并且可以水平和垂直传播。然而，在2018年9月之前韩国没有相关记录。在本研究中，目标是对从患病虹鳟中分离出的FPRT1菌株进行基因型和表型特征分析。我们还进行了各种调查，以更好地了解其影响并评估潜在的控制措施。我们获取了50条虹鳟（体重约70克）并将它们转移到实验室水族箱中。在初始适应期，我们观察死亡率并检查患病鱼的临床症状。我们使用补充有葡萄糖的胰蛋白胨酵母提取物盐琼脂从受感染虹鳟的脾脏中分离出细菌，将其命名为FPRT1。进行了药敏试验，根据结果，我们选择恩诺沙星口服给药给虹鳟以降低死亡率。为了评估致病性，我们在不同水温（8、15和22°C）下使虹鳟接触FPRT1。进行了基因组分析以确定FPRT1的血清型及其与欧洲菌株的亲缘关系。患病鱼表现出临床症状，如下颌溃疡性病变、鳃苍白导致贫血、眼球突出和黏液分泌增加。内部症状包括肝脏苍白和脾脏肿大。FPRT1对红霉素、恩诺沙星、氟苯尼考、土霉素和庆大霉素敏感，但对恶喹酸和磺胺甲恶唑/甲氧苄啶耐药。口服恩诺沙星使死亡率从28%降至6%。致病性试验表明，由于FPRT1在不同温度下导致不同的死亡率。腹腔注射和肌肉注射在8°C时观察到最高死亡率（范围为43%至100%），在22°C时死亡率较低（范围为0%至30%），肌肉注射显示出更高的易感性。基因组分析确定FPRT1为血清型2，并根据核心基因组和可移动基因组表明其与欧洲菌株有密切的遗传关系。我们的菌株与欧洲菌株之间的大量基因组相似性表明细菌可能通过从欧洲进口受精卵传播。总之，本研究突出了此前未记录的病原体（）引入韩国虹鳟种群的情况。这种病原体的检测及其致病性评估不仅对于了解其对当地水产养殖的影响很重要，而且对于建立监测和控制措施以防止该地区进一步传播和爆发也很重要。
