The role of isolation of different streptococcus species in fish pathological lesions

Hosni, Mariam Abdelrhman; Enany, Mohamed; Mabrok, Mahmoud; Yousseff, Fatma M.; Abo Hashem, Marwa E.

doi:10.21608/scvmj.2025.400445.1207

The role of isolation of different streptococcus species in fish pathological lesions

Document Type : Original Article

Authors

¹ Free Veterinarian

² Bacteriology, Immunology and Mycology Department, Faculty of Veterinary Medicine, Suez Canal University.

³ Fish Management and Diseases Department, Faculty of Veterinary Medicine, Suez Canal University, Ismailia, Egypt

⁴ Animal Health Research Institute, Ismailia branch

⁵ Department of Bacteriology, Immunology and Mycology, Faculty of Veterinary Medicie, Suez Canal University, Ismailia, Egypt.

10.21608/scvmj.2025.400445.1207

Abstract

This study investigates the presence of Streptococcus species in Nile tilapia (Oreochromis niloticus) and mullet (Mugil cephalus) collected from aquaculture showing clinical signs of bacterial infection. A total of 25 fish were examined for both external and internal abnormalities such as exophthalmia, skin hemorrhages, fin rot, ocular opacity, and erratic swimming behavior. Samples were aseptically taken from the kidneys, gills, eyes, and heart and cultured on blood agar to evaluate colony morphology and hemolytic patterns. Colonies displaying typical characteristics were subjected to Gram staining and a series of biochemical tests to identify bacterial species. Microscopy revealed Gram-positive cocci in chains or pairs, consistent with the morphology of streptococci and enterococci. The results confirmed the presence of Streptococcus agalactiae and Enterococcus faecalis in the collected samples. This study highlights the concurrent occurrence of these pathogens in farmed fish and emphasizes the importance of accurate diagnosis and strengthened biosecurity measures to minimize bacterial disease outbreaks in aquaculture operations.

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