Induction of Hemagglutinating Activity of Edwardsiella tarda by Sodium Chloride

摘要

The hemagglutinating activity (HA) of Edwardsiella tarda, which had been isolated from cultured fish and culture environments, was investigated in relation to NaCI concentration of the growth medium. E. tarda cells were cultured in a peptone-yeast extract broth supplemented with 3% NaCI (3%-NaCI culture) and without NaCI (0%-NaCI culture). Hemagglutination assays with guinea pig erythrocytes classified the strains into three HA patterns, Seventeen strains exhibited HA only with the 3%-NaCI culture (type A). A more frequent type (35 strains) displayed HA in both 0%- and 3%- NaCI cultures but the 3%-NaCI culture showed higher HA activity than the 0%-NaCI culture (type B). No HA was detected in both cultures of the other three strains (type C). The NaCI-induced HA was well correlated with the expression of a 19.3 kDa protein, a fimbrial major subunit (FimA). Infection experiments with a selected strain (type A) of E. tarda revealed that the 3%-NaCI culture was more virulent to Japanese flounder Paralichthys olivaceus than the 0%-NaCI culture, when fish were challenged by an oral route. This induction of the fimbrial protein under higher NaCI concentration may play an important role in the virulence of E. tarda in marine environments.