Isolation and characterization of a surface layer antigen from Vibrio salmonicida

A cell surface product (VS‐P1) of Vibrio salmonicida has been purified from culture supernatant by a combination of extensive dialysis, filtration and centrifugation, as well as by salt precipitation and hydrophobic chromatography. SDS‐PAGE analysis showed that the monomeric form of the antigen is a single polypeptide with an apparent molecular weight of 40000. Size exclusion HPLC of purified VS‐P1 as well as VS‐Pl‐containing fish serum revealed, however, oligomeric forms in the range from 300000 to more than 700000 daltons. The antigen contained 6% carbohydrate and several isolectric forms were distinguishable when analysed on an analytical isoelectric focusing electrophoresis system. A ‘sandwich’ ELISA, utilizing polyclonal antibodies, was developed for screening sera from both healthy and moribund Atlantic salmon for the presence of the VS‐P1 antigen.