Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Veterinary Medical Sciences - Pathobiological Sciences

First Advisor

Ronald L. Thune


Aeromonas hydrophila and A. sobria have been identified as major causes of mortalities among commercially raised channel catfish and are the cause of septicemic diseases in a wide variety of other animals. At present, antibiotic therapy is the only prescribed treatment for Motile Aeromonad Septicemia (HAS) in channel catfish. Antibiotic treatment, however, is expensive and often not effective due to the development of resistance in the bacterial strains. Development of immunoprophylatic methods for the prevention of HAS would be of value and use to the commercial catfish industry. Several studies have demonstrated that whole cell vaccine preparations do not confer protection to serologically heterologous strains of motile aeromonads. A common antigen needs to be identified among virulent strains of motile aeromonads in order for an efficacious vaccine to be developed. The objective of this study was to determine the role of motile aeromonad virulence factors in natural epizootics of HAS and to determine if particular virulence factors could be used as immunogens. Bacterial isolates collected from channel catfish during HAS epizootics were screened for the production of hemolysins, proteases and surface layer (S-layer) protein. Hemolysin and protease activity were variable and limited among the isolates, but 94% of these isolates produce the S-layer protein. Furthermore, serum antibodies to the S-layer protein from fish immunized with S-layer preparations were detected by western blot analysis. Finally, channel catfish immunized with crude S-layer preparations are protected against subsequent challenge with both the homologous and a heterologous bacterial strain. The S-layer protein may be the common antigen necessary for vaccine development.