PATHOGENICITY OF Streptococcus agalactiae ISOLATED FROM CIRATA, WEST JAVA AND WADAS LINTANG, CENTRAL JAVA IN NILE TILAPIA Oreochromis niloticus
This study was conducted to assess the pathogenicity of Streptococcus agalactiae isolates in Nile tilapia. S. agalactiae isolates, i.e. N3M, N4M, and N17O were collected from Cirata, West Java and NK1 from Wadas Lintang, Central Java. The challenge test using S. agalactiae isolates were performed by injecting the fish with 0.1 mL bacterial suspension (105 CFU/mL) and PBS as the control. Challenge test was conducted for 14 days during which mortality rate, microscopic anatomic pathology, clinical symptoms, and virulence-related genes in S. agalactiae were observed. The virulence genes were detected by polymerase chain reaction (PCR) using specific primers.
The results showed that all S. agalactiae isolates in the present study were pathogenic in tilapia. NK1 was the most virulent S. agalactiae isolate with the highest mortality up to 53.33±5.8% (Table 1). All S. agalactiae isolates tested also caused microscopic changes in the fish liver, brain, and kidneys. Post challenged clinical symptoms of all S. agalactiae isolates infections in tilapia were exopthalmia, opacity, purulens, clear operculum, whirling and bending parts of the body. PCR analysis showed that there were three virulence genes that were found in all S. agalactiae isolates tested, i.e. surface immunogenic protein, sip (339 bp), fibrinogen binding protein, fbsA (420 bp), and factor CAMP, cfb (900 bp). Beta protein C-β, bac (530 bp), however, was not detected in all isolates.
The conclusion of this study indicate that the pathogenicity of N3M, N4M, N17O, and NK1 S. agalactiae isolates are different, but they have similar virulence potential in tilapia.