Diversidad intraespecífica y factores de virulencia en el “complejo de especies de Aeromonas hydrophila” (A. Hydrophila, A. Salmonicida, A. Bestiarum).

Resumen

The genus Aeromonas comprises 26 currently recognized species, some of them divided in to several subspecies. They are ubiquitous in fresh water, but found in chlorinated, brackish and marine water. Aeromonas strains are obtained from a wide variety of foods, as well as clinical samples. Aeromonas species are the cause of intestinal and extra-intestinal infections although the mechanisms that cause bacterial diarrhoea are not yet clearly established. The “A. hydrophila complex” (A. hydrophila, A. salmonicida, A. bestiarum, A. piscicola and A. popoffii), includes A. salmonicida, an important pathogen of fish, and A. hydrophila, an opportunistic pathogen in humans. The virulence of these species is multifactorial and involves complex pathogenic mechanisms associated with toxins (cytotoxic and cytotonic), proteases, haemolysins, lipases, adhesins, agglutinins, pili, etc. A phylogenetic study was performed from a collection of 128 strains belonging to the “A. hydrophila complex", determining partial sequences of dnaJ, cpn60, gyrB and rpoD genes, this analysis allowed us to clarify the taxonomy of this group of Aeromonas species, showing a polyphyletic origin that challenges the existence of the group as such. The population analysis of the studied strains revealed as strong linkage disequilibrium, typical of a clonal population, and a high genetic diversity. We also studied the prevalence and distribution of different virulence factors in the population to establish its pathogenic potential. For this purpose, we determined several enzymatic activities and the antibiotic sensitivity profile of these strains. We also detected the presence of act (aerolysin), alt (cytotonic toxin) and ast (cytotonic toxin) genes by PCR as well as the adhesion capacity and cytopathic effect of the strains on the Caco-2 cell line. The results obtained revealed a high pathogenic of potential the studied Aeromonas strains, regardless of their origin.