Influence of osmolarity on lipopolysaccharides and virulence of Aeromonas hydrophila serotype O:34 strains grown at 37 degrees C.

Growth of Aeromonas hydrophila serotype O:34 strains at 37 degrees C at low and high osmolarity resulted in changes in the lipopolysaccharide (LPS) and virulence of the strains tested. We previously described the effect of growth temperature on LPS and virulence of these strains (S. Merino et al., Infect. Immun. 60:4343-4349, 1992). The effect of osmolarity can be observed when the cells grow at 37 degrees C but not when they grow at 20 degrees C. Purified LPS from cells cultivated at 37 degrees C and high osmolarity was smooth, while the LPS extracted from the cells cultivated at low osmolarity was rough. Furthermore, the strains were more virulent for fish and mice when they were grown at high osmolarity than when they were grown at low osmolarity and also showed increased extracellular activities when they were grown at high osmolarity. Finally, cells grown at high osmolarity showed better adhesion to HEp-2 cells than the same cells grown at low osmolarity, and furthermore the cells grown at high osmolarity were resistant to the bactericidal activity of nonimmune serum, while the same cells grown at low osmolarity were sensitive.