Phenotypic traits,virulence‐associated gene profile and genetic relatedness of Edwardsiella tarda isolates from Japanese eel Anguilla japonica in Korea

Edwardsiella tarda is the predominant bacterium in farm‐cultured eel in Korea. Here, we evaluated the heterogeneity of 37 E. tarda isolates derived from Japanese eel with various origins (olive flounder, common carp and ornamental fish) between 2003 and 2010. Regardless of origins, the biochemical characteristics of E. tarda isolates were homogenous except hydrogen sulfide production, citrate utilization and mannitol fermentation. Based on the phylogenetic analysis of 16S rRNA, E. tarda isolates could be classified into two subgroups and displayed a close relation with Edwardsiella ictaluri and Edwardsiella hosinae lineages, suggesting that the subgroup I has been a predominant type in the Jeonnam and Jeonbuk provinces. I‐CeuI‐based pulsed‐field gel electrophoresis (PFGE) typing showed that the isolates from Japanese eels belonged to 11 pulsotypes, indicating that the presence of highly genomic diversity. Additionally, two isolates, ET‐060 and ET‐191, showed a high frequency of virulence genes (100%) and caused 90% and 60% mortality in Japanese eel, respectively. This finding suggests a substantial congruence of virulence gene profiles and pathogenicity. Our results demonstrate that the intraspecific diversity within E. tarda strains from Japanese eel has been in prior existence.

Significance and Impact of the Study

Based on the biochemical characteristics, the phylogenetic property of the 16S rRNA gene and PFGE types of Edwardsiella tarda, we could identify the intraspecific diversity of isolates from Japanese eel, Anguilla japonica in Korea. In addition, this study describes the strong congruence of virulence‐related genes and pathogenicity, suggesting that the virulence profile may be useful tool for prediction of pathogenicity.