Streptococcosis, lactococcosis and enterococcosis are among the most important bacterial diseases affecting tilapia farms in Kafr Elsheikh governorate, Egypt. A number of clinically diseased fish were collected and submitted to our laboratory during disease outbreak in 2018. They were characterized by nervous swimming behaviour, skin darkness, exophthalmia, ocular opacity and haemorrhages. Necropsy findings were splenomegaly, congestive hepatomegaly, liquefied brain and enteritis. The phenotypic and molecular characterizations of the bacterial strains isolated from naturally infected fish identified three genera of Gram‐positive cocci: Streptococcus agalactiae, Enterococcus faecalis and Lactococcus garvieae. Infectivity trials were conducted in four groups of Nile tilapia inoculated with S. agalactiae Egy‐1, E. faecalis Egy‐1 and L. garvieae Egy‐1 strains and saline. Mortalities, clinical signs and pathological findings were recorded daily 14 days post infection. Experimentally infected tilapia showed similar clinical signs, postmortem lesions, but varied in the severity and experienced high mortalities up to 70% in case of S. agalactiae and L. garvieae infections and 30% in case of E. faecalis infection. Pathological examination of infected tissue sections stained with modified Brown–Brenn and immunohistochemistry revealed an important direct correlation between the distribution of each bacterial isolate and the lesions developed in different organs. Furthermore, the isolates were subjected to profiling against 11 antibiotics, and they showed resistance against several types of antibiotics, which implicate potential risk to human health and emphasize the urgent need for alternate bio‐control strategies to prevent the diseases and the problem of multidrug resistance in aquatic environment.

中文翻译：

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链球菌病，乳球菌病和肠球菌病是养殖尼罗罗非鱼（尼罗罗非鱼）生产面临的潜在威胁

链球菌病，乳球菌病和肠球菌病是影响埃及Kafr Elsheikh省罗非鱼养殖场的最重要细菌病。在2018年的疾病暴发期间，收集了许多临床上有病的鱼并将其提交给我们的实验室。它们的特征是紧张的游泳行为，皮肤黝黑，眼球突出，眼混浊和出血。尸检结果为脾肿大，充血性肝肿大，脑液化和肠炎。从自然感染鱼中分离出的细菌菌株的表型和分子特征鉴定出了革兰氏阳性球菌的三个属：无乳链球菌，粪肠球菌和加维乳球菌。。在接种了无乳链球菌Egy-1，粪肠球菌Egy-1和加维乳杆菌Egy-1菌株和生理盐水的四组尼罗罗非鱼中进行了感染性试验。感染后14天每天记录死亡率，临床体征和病理结果。经实验感染的罗非鱼显示出相似的临床体征，死后病变，但严重程度有所不同，无乳链球菌和加维乳杆菌感染的死亡率高达70％，而粪肠球菌的死亡率高达30％。感染。感染的组织切片经改良的Brown-Brenn染色的病理学检查和免疫组织化学分析显示，每种细菌分离物的分布与在不同器官中发展的病变之间有着重要的直接相关性。此外，对分离物进行了11种抗生素的分析，结果表明它们对几种类型的抗生素具有抗药性，这暗示了对人类健康的潜在风险，并强调了迫切需要替代生物控制策略来预防疾病和多药耐药性问题在水生环境中。