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United States Department of Agriculture

Agricultural Research Service

Title: Antigenicity of Streptococcus Agalactiae Extracellular Products and Vaccine Efficacy

Authors
item Pasnik, David
item Evans, Joyce
item Panangala, Victor
item Klesius, Phillip
item Shelby, Richard
item Shoemaker, Craig

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 14, 2005
Publication Date: April 1, 2005
Citation: Pasnik, D.J., Evans, J.J., Panangala, V.S., Klesius, P.H., Shelby, R.A., Shoemaker, C.A. 2005. Antigenicity of streptococcus agalactiae extracellular products and vaccine efficacy. Journal of Fish Diseases. 28(4):205-212.

Interpretive Summary: Piscine Streptococcus agalactiae infections have been associated with significant morbidity and mortality among freshwater, estuarine, and marine fish species. Pathogenesis in fish involves septicemia and colonization of numerous organs, such as the nares, brain, kidney, and intestines; clinical signs appear soon after infection and include depression or excitability, anorexia, 'C'-shaped body posturing, erratic swimming and whirling, and death. Unfortunately, no chemotherapeutics are approved for treatment of this bacteria. Our laboratory has developed a killed vaccine that can provide tilapia with significant protection against S. agalactiae challenge. However, determination of vaccine stability and potency is vital to satisfy practical product considerations and government regulatory issues. Fish farmers may also wish to vaccinate their fish with the piscine S. agalactiae vaccine at any time during a production cycle or during multiple production cycles, and a vaccine with a long shelf life would therefore be desirable. In the present study, the goal was to determine the efficacy of the S. agalactiae vaccine after storage and to characterize the immunogenic components of S. agalactiae extracellular products (ECP) and their stability in freshly-prepared S.agalactiae vaccine compared to those in one-year stored S. agalactiae vaccine. The specific objectives were to: 1) assess the efficacy of the S. agalactiae vaccine stored for one-year at 4°C, 2) evaluate the production of ECP-specific antibodies and their association to vaccine efficacy following immunization with the freshly-prepared or stored vaccine, and 3) identify ECP antigens from the vaccine recognized by Western blot developed with serum antibodies from tilapia surviving S. agalactiae infection. The stored ECP containing S. agalactiae formalin-killed cells failed to prevent morbidity and mortality among the vaccinated fish. Serum antibody responses of the stored ECP and freshly-prepared ECP against soluble whole cell extract of S. agalactiae indicated that significantly less antibody was produced in fish immunized with stored ECP and S. agalactiae cells than in those fish immunized with freshly-prepared ECP and S. agalactiae cells at Day 31 post-vaccination. Silver staining of SDS-PAGE gels and immunostaining of Western blots with tilapia antiserum to S. agalactiae revealed that predominant 54 and 55 kDa bands were present in the freshly-prepared ECP fraction. The stored ECP revealed the absence of a 55 kDa band and appearance of new bands below 54 kDa on the Western blot. The results of this study on S. agalactiae ECP provides evidence for a correlation between protection and antibody production to ECP and for the importance of the 55 kDa ECP antigen to the vaccine efficacy

Technical Abstract: Streptococcus agalactiae is a major bacterial pathogen that is the cause of serious economic losses in many species of freshwater, marine, and estuarine fish worldwide. A highly efficacious S. agalactiae vaccine was developed using extracellular products (ECP) and formalin-killed whole cells of S. agalactiae. The vaccine efficacy following storage of S. agalactiae ECP and formalin-killed S. agalactiae cells at 4°C for one year was determined. The stored ECP containing S. agalactiae formalin-killed cells failed to prevent morbidity and mortality among the vaccinated fish, and the relative percent survival was 29. Serum antibody responses of the stored ECP and freshly-prepared ECP against soluble whole cell extract of S. agalactiae indicated that significantly less antibody was produced in fish immunized with stored ECP and S. agalactiae cells than in those fish immunized with freshly-prepared ECP and S. agalactiae cells at Day 31 post-vaccination. Silver staining of SDS-PAGE gels and immunostaining of Western blots with tilapia antiserum to S. agalactiae revealed that predominant 54 and 55 kDa bands were present in the freshly-prepared ECP fraction. The stored ECP revealed the absence of a 55 kDa band and appearance of new bands below 54 kDa on the Western blot. The results of this study on S. agalactiae ECP provides evidence for a correlation between protection and antibody production to ECP and for the importance of the 55 kDa ECP antigen to the vaccine efficacy.

Last Modified: 4/20/2014
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