Isolation and molecular characterization of Streptococcus agalactiae recovered from diseased tilapia (Oreochromis sp.)

Abstract

Farmed tilapia with clinical signs such as exophthalmia and external haemorrhages were collected from intensive tilapia/red tilapia farming cages/ponds. Kidney and brain tissues were fixed in neutral buffered formalin solution. The results of histopathological analysis of diseased samples showed characteristics of necrosis due to bacterial infection in the kidney, spleen, and brain. Bacteria were isolated from the kidney, spleen, and brain of fish using brain heart agar. A total of 20 strains were chosen and identified as treptococcus agalactiae bacteria based on morphological, physiological, and biochemical characteristics and positive with specific primers of S. agalactiae. The results of PCR analysis showed that there were 6 isolated strains carrying gene cpsG (272 bp) (serotype 1a), 3 strains carrying 2 genes cpsJ (621 bp) and cpsG (272 bp) (serotype 1b). The remaining strains (11 isolates) carried gene cpsJ (352 bp) (serotype III). The results of this study provide a basis information for further studies to determine the virulence of S. agalactiae strains with different serotypes in tilapia.