G1 antigen: a cell‐surface immunoprotective 96 kDa glycoprotein from the virulent fish pathogen Enterococcus seriolicida, its purification and characterization

Strains of the fish pathogen Enterococcus seriolicida were identified as agglutinating and non‐agglutinating, according to their reaction with anti‐serum raised against type strain YT‐3 (ATCC49156). The non‐agglutinating strains are highly pathogenic in contrast to agglutinating strains. A 96 kDa immunoprotective glycoprotein G1 antigen from non‐agglutinating Ent. seriolicida strain SS91‐014 (N) was purified and characterized. The purification procedure entailed extraction of antigen by glass bead agitation, 80% (NH4)2SO4 precipitation, gel filtration and electroelution. An immunofluorescence microscopy study using monoclonal antibody M3A5 raised against G1 antigen revealed that G1 antigen is present only on the cell surface of non‐agglutinating strains. Therefore, the G1 antigen of virulent Ent. seriolicida could be a potential candidate for protective vaccine against enterococcosis in fish.