Genetic relationships among bacterial strains belonging to the genus Aeromonas were inferred from 16S rRNA, gyrB and rpoB gene sequences. Twenty-eight type or collection strains of the recognized species or subspecies and 33 Aeromonas strains isolated from human and animal specimens as well as from environmental samples were included in the study. As reported previously, the 16S rRNA gene sequence is highly conserved within the genus Aeromonas, having only limited resolution for this very tight group of species. Analysis of a 1?1 kb gyrB sequence confirmed that this gene has high resolving power, with maximal interspecies divergence of 15?2 %. Similar results were obtained by sequencing only 517 bp of the rpoB gene, which showed maximal interspecies divergence of 13 %. The topologies of the gyrB-and rpoB-derived trees were similar. The results confirm the close relationship of species within the genus Aeromonas and show that a phylogenetic approach including several genes is suitable for improving the complicated taxonomy of the genus.

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