The Aeromonas population was organized into 11 clades, which included 2 to 71 strains, with three major clades being observed (bootstrap values ≥ 90). The largest clade was comprised of 71 PX-478 molecular weight isolates,

including 46 human, 5 animal and 20 environmental isolates, among which 4 were reference strains and three were type strains: A. culicicola CIP 107763T, A. ichthiosmia CECT 4486T, A. veronii biovar sobria LMG 13067 and A. veronii biovar veronii CECT 4257T; this was designated the A. veronii clade (Figure 1, Table 1). The two other major clades included 35 and 34 strains, respectively. They were referred to as the A. hydrophila clade (including strains A. hydrophila subsp. hydrophila CECT 839T, A. hydrophila subsp. ranae CIP

107985 and 33 other isolates) and the A. caviae clade (including A. caviae Captisol solubility dmso CECT 838T, A. hydrophila subsp. anaerogenes CECT 4221 and 32 other isolates), respectively. Each of these clades contained strains from various sources, i.e., 25 human, 7 animal and 3 environmental strains in the A. hydrophila cluster and 24 human, 9 environmental and 1 animal isolate in the A. caviae cluster (Figure 1, Table 1). The remaining strains were distributed among eight minor clades (bootstrap values ≥ 90), and are presented in Table 1 and Figure 1. The relative branching order among clades remains uncertain for most nodes (Figure 1). The clades displayed a mean sequence divergence of 2.5%, but the A. media clade displayed higher genetic polymorphism than the other clades (5.8%).

None of the isolates included in this study grouped with the type strains A. bestiarum, A. diversa, A. encheleia, A. enteropelogenes, A. eucrenophila, A. fluvialis, A. popoffi, A. sanarellii, A. schubertii, A. taiwanensis, and A. trota, or with the representative strain of hybridization group 11. Finally, strain CCM 1271 formed an independent phylogenetic branch that was clearly differentiated from related Metalloexopeptidase known species, particularly from A. bestiarum, the species name under which the strain is referenced in the Czech Collection of Microorganisms (Figure 1). A phylogenetic tree reconstructed for all the strains included in this study using a concatenated sequence of the 5 genes obtained for all of the strains also showed strain CCM 1271 to be unrelated to A. bivalvium CECT 7113T , A. molluscorum CIP 108876T , A. simiae CIP 107798T and A. rivuli DSM Doramapimod 22539T (see Additional file 1: Figure S1). Figure 1 Unrooted maximum-likelihood tree based on concatenated sequences of the seven housekeeping gene fragments (3993 nt). The tree shows the structure of the studied Aeromonas spp. population, and the relative placement of human (red font), non-human animal (black font) and environmental (blue font) strains was indicated. The horizontal lines represent genetic distance, with the scale bar indicating the number of substitutions per nucleotide position.