Bacteriological and histopathological studies on Streptococcosis in Nile tilapia, Oreochromis niloticus.

摘要

The aim of this study was to investigate streptococcosis in Nile tilapia, Oreochromis niloticus, in Assiut, Egypt. Thirty-one isolates of Streptococcus faecium could be recovered from 24 fish out of 100 Nile tilapia that were randomly collected from the River Nile and El-Ibrahemia canal at Assiut governorate. Identification was based on colony morphology, culture behaviour in various media, microscopic examination, biochemical tests and carbohydrate fermentation. Experimental infection was successfully done through intraperitoneal injection. The pathognomic signs were petechial haemorrhages on the gill cover, mouth region and fins. Unilateral or bilateral exophthalmia were almost associated with eye haemorrhages. The most common postmortem lesions were pale liver, congestion of spleen, kidneys and gills. The histopathological changes were hydropic degeneration and necrosis of the hepatocytes, depletion of the lymphocytes of the white bulb of the spleen, congestion of the blood vessels of the gills with degeneration of the lamellar epithelium and necrosis of the kidney tissue. Antibiogram sensitivity test for Streptococcus faecium proved that, erythromycin was the drug of choice.