Department of Hydrobiology, Veterinary Research Institute, National Research Centre, 12622, Dokki, Cairo, Egypt.
Fish Diseases Department, Animal Health Research Institute AHRI, Agriculture Research Centre ARC, Kafrelsheikh, Egypt.
Microb Pathog. 2022 Aug;169:105620. doi: 10.1016/j.micpath.2022.105620. Epub 2022 Jun 9.
Edwardsiellosis is a serious bacterial disease affecting Nile tilapia (Oreochromis niloticus), causing septicemia and mortalities. Edwardsiella tarda and Edwardsiella anguillarum were isolated from Nile tilapia summer mortality events in Egypt. Diseased fish showed hemorrhagic septicemia, skin erosions, and eye opacity. A total of 24 Edwardsiella spp. isolates were retrieved from the investigated fish specimens. Phenotypic and biochemical characteristics grouped isolates into typical Ed. tarda (n = 14 strains) and atypical Ed. tarda (n = 10 strains). The BLAST analysis of sodB gene sequencing confirmed the conventional identification of typical Ed. tarda strains (n = 14) and reidentified all the atypical strains (n = 10) as Ed. anguillarum. Isolates showed a combination of virulence factors, including biofilm formation (66.6%), hemolysis (100%), chondroitinase (50%), and proteolytic activity (20.8%). The major part of isolates showed high resistance to ampicillin, amoxicillin, gentamycin antibiotics and harbored tetA, bla and aadA1 resistance genes. Pathogenicity testing of isolates in O. niloticus confirmed their virulence. Challenged fish exhibited septicemic signs similar to naturally diseased fish. Infections in naturally infected tilapia triggered acute and chronic histopathological alterations. Degenerative and necrotic changes were noticed in hematopoietic organs. Granulomas were noticed in between the hepatic parenchyma. The data extracted from the study confirm that accurate identification of the causative agents of edwardsiellosis should be reliant on genetic-based approaches. Analysis of the bacterium virulence properties offers insights into establishing novel therapeutics for edwardsiellosis control. The findings refer to the need for antimicrobial sensitivity testing to minimize antimicrobial resistance and increase therapy efficacy.
爱德华氏菌病是一种严重的细菌性疾病，影响尼罗罗非鱼（Oreochromis niloticus），导致败血病和死亡率。从埃及尼罗罗非鱼夏季死亡事件中分离出迟缓爱德华氏菌和鳗弧菌。患病鱼表现出出血性败血症、皮肤糜烂和眼睛混浊。从调查的鱼标本中总共回收了 24 株爱德华氏菌属分离株。表型和生化特征将分离株分为典型迟缓爱德华氏菌（n=14 株）和非典型迟缓爱德华氏菌（n=10 株）。sodB 基因测序的 BLAST 分析证实了典型迟缓爱德华氏菌株（n=14）的常规鉴定，并重新鉴定了所有非典型菌株（n=10）为鳗弧菌。分离株显示了包括生物膜形成（66.6%）、溶血（100%）、软骨素酶（50%）和蛋白水解活性（20.8%）在内的多种毒力因子。大多数分离株对氨苄西林、阿莫西林、庆大霉素抗生素表现出高耐药性，并携带 tetA、bla 和 aadA1 耐药基因。在 O. niloticus 中对分离株进行的致病性试验证实了它们的毒力。受感染的鱼表现出类似于自然患病鱼的败血症迹象。在自然感染的罗非鱼中引发的感染引发了急性和慢性组织病理学改变。在造血器官中注意到退行性和坏死性变化。在肝实质之间注意到肉芽肿。从研究中提取的数据证实，爱德华氏菌病的病原体的准确鉴定应该依赖于基于遗传的方法。分析细菌的毒力特性可以深入了解建立控制爱德华氏菌病的新疗法。这些发现提到了需要进行抗菌敏感性测试，以最大限度地减少抗菌药物耐药性并提高治疗效果。
