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Title: Vaccination of channel catfish with extracellular products of Aeromonas hydrophila provides protection against infection by the pathogen

Author
item Zhang, Dunhua
item Wei Pridgeon, Yuping
item Klesius, Phillip

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2013
Publication Date: 1/10/2014
Publication URL: http://handle.nal.usda.gov/10113/60513
Citation: Zhang, D., Wei Pridgeon, Y., Klesius, P.H. 2014. Vaccination of channel catfish with extracellular products of Aeromonas hydrophila provides protection against infection by the pathogen. Fish and Shellfish Immunology. 36(1):270-275.

Interpretive Summary: Aeromonas hydrophila secreted many metabolic products (extracellular products or ECP) in milieus during culture or growth, many of which have been attributed to essential factors for the pathogenesis. In this study, ECP of A. hydrophila was prepared from the cell culture and used to vaccinate catfish. Results showed that vaccinated fish could develop immunity against fatal challenge of A. hydrophila. Analysis of the serum of vaccinated fish showed that specific antibody was produced, which could aggregate cells of A. hydrophila and bind specific components in the ECP.

Technical Abstract: Aeromonas hydrophila, a Gram-negative bacterium, is one of the economically-important pathogens in modern aquaculture. Among various traits, extracellular products (ECP) secreted by the bacterium are considered to be essential factors for virulence. Whether vaccination with the ECP could produce immune protection in catfish against the pathogen was determined in this study. The results showed that fish vaccinated with ECP had 100% of relative percent survival (RPS) when challenged with the pathogen two weeks post vaccination. The anti-ECP serum from vaccinated fish could aggregate the homogeneous bacterial cells as well as other virulent strains (isolates) of A. hydrophila but not an A. veronii isolate and a low virulent field isolate. The agglutination titers increased from two weeks to four weeks post immunization and sustained a high level at week seven when the RPS remained at 100%. The anti-ECP serum could also provide naïve fish with immediate protection against A. hydrophila as evidenced by passive immunization. Immunoblotting analysis further showed that the anti-ECP serum contained antibodies that bound to specific targets, including lipopolysaccharide-like molecules, in the ECP. Findings revealed in this study suggest that, while ECP prepared in a conventional and convenient way could be a vaccine candidate, identification and characterization of antibody-mediated targets in the ECP would uncover quintessential antigens for the future development of highly efficacious vaccines.