Immunogenic Potential of Growth Products Extracted from Cultures of Aeromonas salmonicida for Brook Trout (Salvelinus fontinalis)
Growth products from virulent (3.93 and 3.101), an avirulent (3.10), and an atypical strain (3.111) of Aeromonas salmonicida yielded four 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 four fractions from a virulent and an avirulent strain were injected intraperitoneally at a dose of 5 μg protein into brook trout (Salvelinus 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 two 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 approximate molecular weight of 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.Key words: Aeromonas salmonicida, Salvelinus fontinalis, growth products, fraction 4, glycoprotein, virulent, avirulent, atypical strains, contact experimental challenge