Genetic relationships of Edwardsiella strains isolated in China aquaculture revealed by rep-PCR genomic fingerprinting and investigation of Edwardsiella virulence genes

Aims: The aim of this study was to classify Edwardsiella strains isolated from China aquaculture based on biochemical and molecular methods. Methods and Results: In this study, biochemical characterization of 19 Edwardsiella tarda isolates and two Edwardsiella ictaluri isolates was performed with API 20E system. Other pathogenicity‐related phenotypes such as haemagglutination, haemolytic activities and lethality to fish were also examined in these strains. As it was difficult to categorize the subgroups of Edw. tarda according to their origins or phenotypic properties, three PCR‐based methods, i.e. PCR amplification of virulence genes, Enterobacterial repetitive intergenic consensus‐PCR and BOX‐PCR, were carried out to further resolve the relatedness of the Edw. tarda isolates. As a result, all Edw. tarda isolates could be generally grouped into pathogenic and nonpathogenic branches before being classified into strain‐specific or origin‐specific clades. Conclusions: Biochemical characterization was sensitive for interspecific typing, while PCR‐based approaches permitted a more accurate discrimination for intraspecific typing resulting in pathogenic and nonpathogenic clusters and further more delicate clades for Edwardsiella. Significance and Impact of the Study: PCR‐based genomic fingerprinting to study the relatedness and trace the pathogenicity of the Edwardsiella strains will be helpful in investigating the virulence factors of Edwardsiella and in the development of vaccines and diagnostics for edwardsiellosis.