Prevalence, virulence-gene profiles, antimicrobial resistance, and genetic diversity of human pathogenic Aeromonas spp. from shellfish and aquatic environments*

Aeromonas are found in various habitats, particularly in aquatic environments. This study examined the presence of the most common human pathogenic Aeromonas species (Aeromonas caviae, A. hydrophila, and A. veronii) in surface water, sea water, and shellfish. The detection rates in fishing harbour seawater, shellfish farming seawater, and a river basin were 33.3%, 26.4%, and 29.4%, respectively, and high prevalence was observed in summer. The detection rates in shellfish procured from a fish market and shellfish farm were 34.9% and 13.3%, respectively. The most abundant species of human pathogenic Aeromonas detected via water sampling was A. caviae, whereas that obtained via shellfish sampling was A. veronii. The prevalence of human pathogenic Aeromonas in river water was lower in fishing harbours and in the estuary shellfish farming area. Here, 25 isolates of human pathogenic Aeromonas species were isolated from 257 samples and divided among 16 virulence profiles. The high virulence gene-carrying isolates (more than six genes) belonged to A. hydrophila. The shellfishsourced isolates had the highest detection rates of act, aerA, and fla genes than of other virulence genes, and vice versa for seawater-sourced isolates. The Aeromonas isolates showed high levels of resistance to ampicillinsulbactam; however, none were resistant to cefepime, ciprofloxacin, or gentamicin. The incidence of multiple drug resistance (MDR) in Aeromonas isolates was 20%. In this study, phylogenetic analysis with 16S rRNA sequencing, biochemical tests and enterobacterial repetitive intergenic consensus-polymerase chain reaction fingerprinting facilitated the distinct categorisation of three species of human pathogenic Aeromonas isolates. In addition, A. veronii isolates from the same geographical area were also concentrated in the same cluster. This study provides information on the risk of infection by Aeromonas with MDR and multiple virulence genes isolated from shellfish and aquatic environments.