Passive transfer of serum from tilapia vaccinated with a Vibrio vulnificus vaccine provides protection from specific pathogen challenge

• Antiserum was generated by vaccination of tilapia with a Vibrio vulnificus bacterin.
• Passive transfer of antiserum conferred protective immunity against V. vulnificus challenge.
• Antiserum exhibited antibodies specific for protein and lipopolysaccharides.
• Results supported a role of specific antibodies in the protection of tilapia against V. vulnificus.

Vibrio vulnificus is a Gram-negative bacterium that has been associated with disease losses in some aquaculture reared fish species. Vaccination has proven effective for reducing the impact of this disease and research has suggested that specific antibodies are important for protective immunity. The present study determined the role of antibodies specific for V. vulnificus in protection by passive immunization and identified components of the bacterium the antibodies specifically recognize. Antiserum was generated by vaccinating hybrid tilapia with a formalin killed V. vulnificus ARS-1-Br-09 bacterin. Two passive immunization experiments were conducted, with and without heat inactivation of the antiserum. In both experiments, hybrid tilapia (mean weight, 6.5 g) were passively immunized by intraperitoneal injection of antiserum or control serum and then challenged with homologous V. vulnificus 24 h post-immunization. Following the challenge, relative percent survival values of 86 and 90 were obtained for tilapia passively immunized with non-heated and heat inactivated antiserum, respectively. Cell lysates and lipopolysaccharide preparations from V. vulnificus ARS-1-Br-09 and a heterologous isolate (CECT 4601) were probed with the antiserum and control serum by western blot analyses to determine the specificity of the antibodies. The antibodies exhibited specificity to proteins of both isolates and to the lipopolysaccharide of only the homologous isolate. The results supported a role of specific antibodies in the protection of tilapia against V. vulnificus, and suggested that shared immunogenic antigens were involved in protection previously described against heterologous isolates.