Immune response of channel catfish to ipopolysaccharide and whole cell Edward-siella ictaluri vaccines

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Abstract
The efficacy of Edwardsiella ictaluri lipopolysaccharide (LPS) and of formalin-killed E. ictaluri whole cell bacterins was investigated in channel catfish Ictalurus punctatus. Vaccine efficacy was measured in terms of serum agglutinin production and enhanced immunity to experimental challenge with the pathogen. Mutiple injections of LPS in Freund''s complete adjuvant (FCA) produced higher antibody titers (1391) than multiple injections of LPS in saline (131), and protection conferred by the former technique was also greater (3.3 vs 36.7% mortality while unvaccinated controls suffered 70% mortality). Single injections of LPS in FCA also produced high agglutination titers (2048), but protection was less than that obtained with multiple injections in FCA (20 vs 3.3% mortality). Multiple injections of whole cells in FCA produced high titers (2730) and strong protection (8.3 % mortality). Single injections of the whole cells also yielded respectable titers (1220) and some protection (31.1%). Multiple and single injections of the bacterin in saline resulted in modest antibody levels and no protection. Injected FCA alone, and vaccination by immersion (single and multiple dips, with and without hyperosmotic pretreatment) yielded no protection. These results indicate that E. ictaluri LPS preparations are capable of enhancing immunity against E. ictaluri, but practical methods for administering the vaccine must still be found.

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