Department of Aquatic Animal Medicine and Management, Faculty of Veterinary Medicine, Assiut University, Assiut, 71529, Egypt.
Poultry and Fish Diseases Department, Faculty of Veterinary Medicine, Minia University, Minia, 61519, Egypt.
BMC Vet Res. 2024 Oct 15;20(1):468. doi: 10.1186/s12917-024-04298-z.
Streptococcus agalactiae (Group B streptococcus, GBS) induces a serious infection that can harm not only aquatic life but also humans and other animals. In a fish farm in southern Egypt, Nile tilapia (Oreochromis niloticus) has developed an epidemic with clinical symptoms resembling piscine streptococcosis.
Initial microscopic inspection of the affected fish brain and kidney indicated the presence of Gram-positive cocci. S. agalactiae was effectively isolated and identified using nucleotide homology of the 16S rRNA and species-specific PCR. The partial 16S rRNA sequence was deposited in the GenBank database at the NCBI and given the accession number MW599202. Genotyping using RAPD analysis indicated that the isolates in the present study belonged to the same genotypes and had the same origin. The challenge test, via immersion (9.2 × 10, 9.2 × 10, and 9.2 × 10 CFU/ml for 1 h) or intraperitoneal injection (4.6 × 10, 4.6 × 10, and 4.6 × 10 CFU/fish), elicited clinical symptoms resembling those of naturally infected fish with a mortality rate as high as 80%. The ability to create a biofilm as one of the pathogen virulence factors was verified. Zinc oxide nanoparticles and the ethanolic leaf extracts of nine medicinal plants demonstrated considerable antibacterial activities against the tested S. agalactiae strain with low minimum bactericidal concentrations (MBC) and minimum inhibitory concentrations (MIC). The ethanolic leaf extracts from Lantana camara and Aberia caffra showed potent antibacterial activity with MBC values of 0.24 and 0.485 mg/ml, and MIC values of 0.12 & 0.24 mg/ml, respectively.
This study isolated S. agalactiae from O. niloticus mortalities in a fish farm in Assiut, Egypt. The pathogen persists in fish environments and can escape through biofilm formation, suggesting it cannot be easily eliminated. However, promising findings were obtained with in vitro control employing zinc oxide nanoparticles and medicinal plant extracts. Nevertheless further in vivo research is needed.
无乳链球菌（B 群链球菌，GBS）可引起严重感染，不仅危害水生生物，还危害人类和其他动物。在埃及南部的一个养鱼场，尼罗罗非鱼（Oreochromis niloticus）发生了一种具有类似鱼链球菌病临床症状的流行疫病。
对患病鱼脑和肾脏的初步显微镜检查表明存在革兰氏阳性球菌。通过核苷酸同源性的 16S rRNA 和种特异性 PCR 有效分离和鉴定了无乳链球菌。部分 16S rRNA 序列在 NCBI 的 GenBank 数据库中进行了注册，并获得 MW599202 登录号。通过随机扩增多态性 DNA（RAPD）分析进行的基因分型表明，本研究中的分离株属于相同的基因型，具有相同的来源。通过浸泡（9.2×10、9.2×10 和 9.2×10 CFU/ml 持续 1 小时）或腹腔注射（4.6×10、4.6×10 和 4.6×10 CFU/鱼）进行的攻毒试验，诱发了类似于自然感染鱼的临床症状，死亡率高达 80%。验证了作为病原体毒力因子之一的生物膜形成能力。氧化锌纳米粒子和 9 种药用植物的叶乙醇提取物对测试的无乳链球菌菌株表现出相当大的抗菌活性，最低杀菌浓度（MBC）和最低抑菌浓度（MIC）较低。Lantana camara 和 Aberia caffra 的叶乙醇提取物具有很强的抗菌活性，MBC 值分别为 0.24 和 0.485 mg/ml，MIC 值分别为 0.12 和 0.24 mg/ml。
本研究从埃及阿西尤特的一个养鱼场的 O. niloticus 死亡鱼中分离出无乳链球菌。病原体在鱼类环境中持续存在，并可通过生物膜形成逃脱，这表明其不易消除。然而，体外控制采用氧化锌纳米粒子和药用植物提取物取得了有希望的结果。然而，需要进一步的体内研究。
