Altogether, our results confirm those of a previous study comparing genomic profiles of clinical isolates of Aeromonas salmonicida using DNA microarrays [32]. With the origin and intensification

of fish farming, genetic rearrangements occurring through IS transposition events could have been responsible for the selection and the emergence of this pathogenic fish specific clone. Such an adaptation process of a pathogenic bacterium towards its host was recently indicated Peptide 17 research buy in the Mycoplasma mycoides cluster for Mycoplasma mycoides subsp. mycoides[33]. Moreover, no unique pattern was associated to a specific geographical region of the world and we assume that this could be explained by the dissemination of A. salmonicida subsp. salmonicida strains between aquaculture countries via the intensification of the international trade in farmed salmon or by the natural migration of wild salmons. Besides the epidemiologic and phylogenetic interests of IS630 fingerprinting to subtype A. salmonicida, we studied the characteristics of this predominant IS element to reveal information concerning the pathoadaptation towards its specific host. Mobile genetic elements can exert different effects GSK126 supplier on bacterial genomes

[11, 34–36]. Through such genomic effects, IS630 family has had an impact on the modulation of virulence genes in other bacteria [37–43]. In A. salmonicida 90% of the IS630 copies reside in genomic regions that are variable between Aeromonas sp. (Additional file 1: Table S1) and 80% of these sites contain genes that are specific to A. salmonicida and are not encountered in other Aeromonas sp. suggesting that they constitute genomic islands. A part

of these coding sequences are phages or hypothetical genes with homologues of characterized sequences in other environmental bacteria: i.e. the ‘Vibrio Seventh Pandemic cluster I’ (VSP-I), genes for the synthesis of polysaccharide capsule, lipopolysaccharide, S-layer, chitinase, cytolytic insecticidal delta-endotoxin, and some effectors (AopO and ApoH) of the type-three C-X-C chemokine receptor type 7 (CXCR-7) secretion system, the major virulence system of the bacterium. Based on these findings we assume that IS630 elements could be used by environmental bacteria to exchange DNA fragments between each other by horizontal transfer. In the genomic islands where IS630 is present, supplementary IS elements can be found, which might serve as hot spots for further insertions. This would allow the transposon and the genomic island to evolve with acquisition of new genes without disruption of existing loci. These observations could explain why the IS630 elements remained stable within the A. salmonicida subsp. salmonicida genome. Other interesting characteristics of IS elements homologous to IS630 in A.