The role of the capsular polysaccharide of Aeromonas hydrophila serogroup O:34 in the adherence to and invasion of fish cell lines.

The ability of Aeromonas hydrophila serogroup O:34 strains grown under different conditions (capsulated and non-capsulated) to adhere to and invade two fish cell lines was compared. The level of adherence was slightly higher when the strains were grown under conditions promoting capsule formation than when the same strains were grown under conditions which did not promote capsule formation. However, the most significant difference among the wild-type strains grown under conditions promoting capsule formation was the ability to invade the fish cell lines, which was significantly higher than when the same strains were grown under conditions which did not promote capsule formation. Isogenic unencapsulated mutants grown under conditions promoting capsule formation showed a lower ability to invade the fish cell lines than the parental capsulated strains. From these results, we concluded that the capsular polysaccharide is an important factor in intracellular invasion.