Submitted to: American Fisheries Society Transaction
Publication Type: Abstract Only
Publication Acceptance Date: June 15, 2005
Publication Date: July 27, 2005
Citation: Pasnik, D.J., Evans, J.J., Panangala, V.S., Klesius, P.H., Shelby, R.A., Shoemaker, C.A. 2005. Immunogenicity of a streptococcus agalactiae vaccine: the role of extracellular antigens and antibodies. 2005 Annual Meeting of the Fish Health Section/American Fisheries Society Transaction July 27-29, 2005. Minneapolis, MN. Abstract p. 37. Technical Abstract: Though Streptococcus agalactiae has been associated with serious economic fish losses worldwide, no commercial fish vaccines against this pathogen are currently available. A highly efficacious S. agalactiae vaccine was developed using S. agalactiae extracellular products (ECP) and formalin-killed whole cells. Two experiments were conducted using Nile tilapia, Oreochromis niloticus, to determine the mediators involved in the conferred protection against S. agalactiae. One study assessed the vaccine efficacy of stored reconstituted S. agalactiae vaccine, which failed to significantly (p = 0.19) prevent morbidity and mortality among the vaccinated fish. Serum antibody responses of fish inoculated with stored ECP and freshly prepared ECP indicated that significantly less (p < 0.0001) anti-S. agalactiae antibody was produced in fish immunized with stored vaccine. Silver staining of sodium dodecyl sulfate polyacrylamide gels and immunostaining of Western blots with tilapia antiserum to S. agalactiae revealed predominant 54 and 55 kDa bands in the freshly prepared ECP fraction. The 55 kDa band was absent from the stored ECP and new bands below 54 kDa appeared on the Western blot. Another vaccine study was conducted to determine the duration of protection and its correlation to antibodies specific for this pathogen. Fish were injected with fresh vaccine and challenged with S. agalactiae 47, 90, or 180 days post-vaccination (DPV), and the percent survival among vaccinated fish was significantly higher (p < 0.05) than for controls at each time point. The specific mean antibody concentration of the vaccinated fish was significantly higher (p < 0.05) than in controls with significant correlation (r2 = 0.7923, 0.5712, and 0.8828 on 47, 90, and 180 DPV, respectively) between increased ELISA optical densities (OD) and protection. These results indicate that the specific antibody has a correlation with protection following immunization with fresh vaccine and that the vaccine conferred protection against S. agalactiae for at least 180 days after vaccination. The results of both studies provide evidence for a correlation between protection and antibody production to ECP and for the importance of the 55 kDa ECP antigen for vaccine efficacy.