Fish diseases caused by bacterial genera belonging to the family Flavobacteriaceae, especially Tenacibaculum, Flavobacterium, and Chryseobacterium, are responsible for losses in wild and farmed fish around the world. In the last decade, the genus Chryseobacterium has rapidly grown in parallel with numerous novel Chryseobacterium species described from systemic infections of fish. Members of the family Flavobacteriaceae, isolated from fish, the environment, and clinical samples, have been reported to show low susceptibility to a broad range of antimicrobials. In this study, seventy C. aquaticum strains were isolated from diseased salmonids in Turkey. The phylogenetic analysis of all C. aquaticum strains, together with the reference strains in GenBank, which were obtained from different sources, including fish, plants, soil, water, and other animals, was performed by 16S rRNA gene sequence analysis. The antimicrobial susceptibility of each C. aquaticum strain was determined by a minimum inhibitory concentration (MIC) test. The isolate with the highest level of antimicrobial resistance, strain C-174, underwent a more detailed whole-genome sequence analysis for virulence and antimicrobial resistance genes (AMR) genes, genome size, and guanine-cytosine (GC) content.

Phylogenetically, the 70 strains isolated from Turkey were assigned to three genogroups. Strains previously recovered from the rainbow trout, brown trout, and Siberian sturgeon were genetically very close to our strains. Most of the strains isolated in this study grew even in the presence of high concentrations of the tested antimicrobials, excluding enrofloxacin. Strain C-174 carried 74 putative functional genes encoding AMR and virulence. The number of putative AMR genes detected in the genome of strain C-174 was 46. The regulatory mechanisms of these genes involve antibiotic efflux (13), antibiotic target alteration (17), antibiotic inactivation (7), antibiotic target replacement (3), and antibiotic target protection (6). AMR genes confer resistance to multiple antibiotic groups, including among others, macrolides, fluoroquinolones, beta-lactams, tetracyclines, phenicols, sulphonamides, and diaminopyrimidines. We concluded that antimicrobial resistance could be of intrinsic nature. Furthermore, we detected three putative virulence genes in the genome of strain C-174 that have not been reported for C. aquaticum before. The results of this study demonstrated a strong correlation between these genes in the genome of C-174 and mortality in the rainbow trout.

由属于家庭细菌属鱼病黄杆菌，尤其是黏着，黄杆菌和金黄，负责在野生和养殖鱼类在世界各地的损失。在过去十年中，属金黄杆菌中与许多新颖平行增长迅速金黄从鱼的全身性感染中描述的物种。据报道，从鱼类，环境和临床样品中分离出的黄杆菌科成员对多种抗菌素的敏感性较低。在这项研究中，七十个水生C. aquaticum从土耳其患病的鲑鱼中分离出菌株。通过16S rRNA基因序列分析，对所有水生梭状芽胞杆菌菌株以及GenBank中的参考菌株进行了系统发育分析，这些菌株来自不同的来源，包括鱼类，植物，土壤，水和其他动物。通过最小抑制浓度（MIC）测试确定每个水生梭状芽胞杆菌菌株的抗药性。具有最高水平抗药性的分离株C-174进行了更详细的全基因组序列分析，以分析毒力和抗药性基因（AMR）基因，基因组大小和鸟嘌呤-胞嘧啶（GC）含量。

在系统发育上，从土耳其分离的70个菌株被分为三个基因组。以前从虹鳟鱼，褐鳟鱼和西伯利亚st鱼中恢复的菌株在基因上与我们的菌株非常接近。这项研究中分离出的大多数菌株即使在高浓度的测试抗菌药物（恩诺沙星除外）的存在下也能生长。C-174菌株携带74个假定的编码AMR和毒力的功能基因。在菌株C-174的基因组中检测到的推定AMR基因数量为46。这些基因的调控机制涉及抗生素外排（13），抗生素靶点改变（17），抗生素失活（7），抗生素靶点替代（3）。 ，以及抗生素靶向保护（6）。AMR基因可赋予多种抗生素抗药性，其中包括大环内酯类，氟喹诺酮类，β-内酰胺，四环素，苯甲酚，磺酰胺和二氨基嘧啶。我们得出的结论是，抗菌素耐药性可能是固有的。此外，我们在菌株C-174的基因组中检测到三个尚未报道的致病性基因C. aquaticum之前。这项研究的结果表明，C-174基因组中的这些基因与虹鳟鱼的死亡率之间具有很强的相关性。