Multilocus genetics to reconstruct aeromonad evolution
1 Laboratoire de Bactériologie-Virologie (UMR 5119 - Equipe Pathogènes et Environnements), Université Montpellier 1, 15, Avenue Charles Flahault, BP 14491, 34093, Montpellier Cedex 5, France
2 Laboratoire de Bactériologie, Centre Hospitalier Régional Universitaire de Montpellier (Hôpital Arnaud de Villeneuve), 371, Avenue du Doyen Gaston Giraud, 34295, Montpellier Cedex 5, France
3 Laboratoire d’Hygiène hospitalière, Centre Hospitalier Universitaire de Montpellier, 778, Rue de la Croix Verte, 34000, Montpellier, France
4 CNRS UMR 5557 Ecologie microbienne, VetAgro Sup Campus vétérinaire de Lyon, 69280, Marcy-l’Étoile, France
5 Groupe d’ Etude Français des Aeromonas (GFA), Lyon, France
6 ColBVH, Collège de bactériologie, virologie et hygiène des hôpitaux généraux, Lyon, France
BMC Microbiology 2012, 12:62 doi:10.1186/1471-2180-12-62Published: 30 April 2012
Aeromonas spp. are versatile bacteria that exhibit a wide variety of lifestyles. In an attempt to improve the understanding of human aeromonosis, we investigated whether clinical isolates displayed specific characteristics in terms of genetic diversity, population structure and mode of evolution among Aeromonas spp. A collection of 195 Aeromonas isolates from human, animal and environmental sources was therefore genotyped using multilocus sequence analysis (MLSA) based on the dnaK, gltA, gyrB, radA, rpoB, tsf and zipA genes.
The MLSA showed a high level of genetic diversity among the population, and multilocus-based phylogenetic analysis (MLPA) revealed 3 major clades: the A. veronii, A. hydrophila and A. caviae clades, among the eleven clades detected. Lower genetic diversity was observed within the A. caviae clade as well as among clinical isolates compared to environmental isolates. Clonal complexes, each of which included a limited number of strains, mainly corresponded to host-associated subsclusters of strains, i.e., a fish-associated subset within A. salmonicida and 11 human-associated subsets, 9 of which included only disease-associated strains. The population structure was shown to be clonal, with modes of evolution that involved mutations in general and recombination events locally. Recombination was detected in 5 genes in the MLSA scheme and concerned approximately 50% of the STs. Therefore, these recombination events could explain the observed phylogenetic incongruities and low robustness. However, the MLPA globally confirmed the current systematics of the genus Aeromonas.
Evolution in the genus Aeromonas has resulted in exceptionally high genetic diversity. Emerging from this diversity, subsets of strains appeared to be host adapted and/or “disease specialized” while the A. caviae clade displayed an atypical tempo of evolution among aeromonads. Considering that A. salmonicida has been described as a genetically uniform pathogen that has adapted to fish through evolution from a variable ancestral population, we hypothesize that the population structure of aeromonads described herein suggested an ongoing process of adaptation to specialized niches associated with different degrees of advancement according to clades and clusters.