Surface antigens of virulent strains of Aeromonas hydrophila

Antiserum was raised in rabbits to whole cells of a representative strain from a group of A. hydrophila strains exhibiting enhanced virulence for fish. The major surface antigens of the strain were identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. The lipopolysaccharide (LPS) was examined using SDS-PAGE and silver staining. It was found to possess O polysaccharide chains of homogeneous length that were highly immunogenic. The LPS was conserved both morphologically and antigenically throughout the high virulence group. Heat-labile protein antigens were detected after absorption of the antiserum with boiled cells of the homologous strain. Only one major protein antigen, with a molecular weight of approximately 52,000, was present in outer membrane preparations or in whole cell lysates. A representative strain from the high virulence group, strain TF7, was shown by electron microscopy to be covered by a regular surface protein array (S-layer) which was found to be composed primarily of the 52 KD protein antigen. All the other members of the A. hydrophila high virulence group were shown to possess similar S-layers.