Immunogenic Potential of Growth Products Extracted from Cultures of Aeromonas salmonicida for Brook Trout (Salvelinus fontinalis)

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Abstract
Growth products from virulent (3.93 and 3.101), an avirulent (3.10) and an atypical strain (3.111) of A. salmonicida yielded 4 protein containing fractions (designated fractions 1,2,3,4) following chromatography on DEAE Sephadex A-25 of crude material that was precipitated from broth culture supernatants with (NH4)2SO4 and ethanol. Vaccination trials, in which each of the 4 fractions from a virulent and an avirulent strain were injected i.p. at a dose of 5 .mu.g protein into brook trout (S. fontinalis) indicated that only fraction 4 consistently protected trout from experimental challenges. Immunizing fish with fraction 4 that was emulsified in Freund''s incomplete adjuvant also protected trout from challenge but did not enhance protection. Additional brook trout that were immunized by injection with fraction 4 derived from either of 2 virulent, an avirulent or an atypical strain of A. salmonicida were also protected from contact challenge with a different challenge strain. Fraction 4 was partially characterized as a glycoprotein; the protein subunit fraction had an MW of .apprx. 66,000 daltons. Rabbit antiserum prepared against fraction 4 reacted on agar gel diffusion plates to form a single precipitin band with the homologous fraction 4 antigen but this antiserum did not cross react with either purified preparations of bacterial endotoxin or A-layer protein.

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