Characterization of Edwardsiella Strains Isolated from Fish in The Netherlands (1995-2020) Shows a Relationship Between Edwardsiella Species and Source.

To date, four species of the genus Edwardsiella-E. tarda, E. ictaluri, E. piscicida, and E. anguilarum-have been identified as the cause of disease and mortality in various fish species. Thirty-six Edwardsiella strains isolated from different fish species in the Netherlands were identified using multilocus sequence analysis (MLSA) based on sequence analysis of the genes gyrB, pgi and phoU. In parallel, an Edwardsiella matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) database was created by analyzing peptide spectra of a subset of these strains belonging to the four fish pathogenic species. MALDI-TOF MS analysis of the Edwardsiella isolates using the newly created database revealed 100% agreement with results of MLSA. Moreover, the presence of each Edwardsiella species was associated with specific fish host and source, with E. piscicida being the dominant species in Dutch aquaculture. In addition, a novel strain was isolated from electric eel, genetically diverging from the four established species. Whole-genome comparisons of the novel strain with those species showed DNA-DNA hybridization and average nucleotide identity scores suggestive of a new species. In conclusion, both MLSA and MALDI-TOF analysis can be used to identify Edwardsiella species. Moreover, it has been observed that different Edwardsiella species show a preference for certain hosts or sources.