Iron-acquisition Ability of Edwardsiella tarda with Involvement in Its Virulence.

Abstract

Forty-one strains of Edwardsiella tarda including both virulent and avirulent strains were examined in their iron-acquisition ability. The strains were divided into two groups by growth under an iron-Iimiting condition (LB broth containing casamino acid in the presence of 6.25 μm EDDHA); one group was able to grow more than 102 times the initial bacterial density, but the other was not. The bioassay and the modified CAS assay for detecting bacterial siderophore production showed that the strains of the former group produced the siderophore with a higher ability for ironacquisition than those of the latter group. The siderophore-producing strains include all virulent ones. In addition, a natural mutant that showed lowered siderophore production had a remarkably reduced virulence. All of strains produced two outer membrane proteins, one of which is considered to be a receptor of the siderophore under the iron-limiting condition, indicating that these proteins are hardly related to the virulence of E. tarda. Our data in the present study suggest that the iron-acquisition ability of E. tarda by the siderophore is involved in its virulence.