Comparison of Cellular and Extracellular Products Expressed by Virulent and Attenuated Strains of Edwardsiella ictaluri

Abstract

Cellular and extracellular products of three virulent Edwardsiella ictaluri isolates were compared with corresponding attenuated strains to evaluate potential virulence factors. The characteristics compared included growth kinetics, hemolysin activity, surface structures, outer membrane protein profiles, and lipopolysaccharide profiles. To produce the attenuated strains, we passed three isolates through multiple subcultures in liquid media. Attenuated strains were found to have shorter generation times than virulent strains. They also apparently failed to express a 55-kdalton outer membrane protein that the virulent strains possessed. Scanning electron microscopy found no conclusive differences in surface structure expression. Hemolysin activity was significantly greater in virulent strain R4383 than in its corresponding attenuated strain. Lipopolysaccharide profiles showed no apparent differences in the O polysaccharide portion; however, the composition of core oligosaccharide sugars differed between the two.