Characterization of Edwardsiella ictaluri Isolated from Wild Ayu Plecoglossus altivelis in Japan

A Gram-negative bacterium was isolated from diseased wild ayu Plecoglossus altivelis, which were caught in rivers in Japan from August to October in 2007. All four isolates examined showed the same morphological, physiological and biochemical characteristics and were classified into the genus Edwardsiella. The isolates were differentiated from E. tarda in respect of its negative production of indole and no growth at 37°C, and different from a reference strain of E. ictaluri (JCM1680) in its positive production of hydrogen sulfide. All isolates were completely identical in the partial nucleotide sequences of 16S rDNA, a type 1 fimbrial gene (etfA) and a heat shock protein gene (dnaJ), and these sequences showed high similarity (100%, 99.7% and 100%, respectively) with E. ictaluri but low similarity (99.7%, 92.5% and 87.3%, respectively) with E. tarda. Based on these phenotypic and genetic characteristics, the present isolates from ayu were identified as E. ictaluri.