Author(s): Md. Mer Mosharraf Hossain, Md. Anisur Rahman, Hironmoy Sovon Roy, Ibrahim Kholil, Md. Hasan-Uj-Jaman and Md. Eftakher Alam

Abstract: Streptococcus iniae is an important pathogen that can cause a broad range of disease in aquatic animals. To avoid the use of antibiotics and drugs, it is critical to identify protective antigens for developing highly effective vaccines against this pathogen. Vaccination is the most effective means of preventing infectious diseases; however, few vaccines are effective against Streptococcus iniae (S. iniae) in mono-sex Nile Tilapia. This work presents an efficacious and safe vaccine against S. iniae infections in monosex Nile tilapia (Oreochromis niloticus). The vaccine candidate was the S. iniae F-1 strain. The vaccination was administered by intraperitoneal injection, and consisted of inactivated antigens; both the vaccinated and non-vaccinated fishes were challenged intraperitoneally with S. iniae (1 × 10⁷ CFU ml−¹) isolates and PBS (negative control). Peripheral blood samples were collected for SDS-PAGE, phagocytosis and agglutination assays. Present results indicated that immunoglobulin M (IgM) was maximally expressed in the low-amperage electric current inactivated (ECKC) vaccinated group at 3 months post-secondary vaccination (PSV). Phagocytic activity and index increased significantly in (ECKC) vaccinated group. Furthermore, fish in (ECKC) vaccinated group exhibited significantly elevated agglutination titers compared to fish in the control group, in which almost no agglutination reaction was detected. In the efficacy test, the vaccinated fishes had a significant increase in RPS (69 and 89, respectively); the percentage mortality declined from 83 ± 0.6 and 74 ± 0.7 in challenged and control fishes to 25% ± 0.8% and 8% ± 0.8% in vaccinated and challenged fish groups, respectively. Furthermore, the level of protection observed in the field trial closely resembled that achieved on a laboratory scale. Therefore, EC-killed showed the highest molecular weight 31 kDa in SDS-PAGE and Western blot and increased RPS (91%), suggested that the EC-killed cells of S. iniae could play an important role in immunizing monosex Nile tilapia. The EC-killed cells of S. iniae will may safe and long-lasting protection against streptococcosis.

DOI: 10.22271/fish.2016.v4.i4b.826

Pages: 99-105  |  1547 Views  120 Downloads

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