Prevalence and virulence potential of Aeromonas spp. isolated from human diarrheal samples in North East Italy

Aeromonas spp. are emerging human pathogens causing intestinal and extra-intestinal infections. Since their relevance in Western Europe as gastrointestinal pathogens is not well established, we investigated Aeromonas spp. prevalence in diarrheal fecal samples in an Italian University Hospital and characterized the virulence mechanisms of the isolates. Aeromonas spp. isolated from diarrheic stools using standard culture methods were identified by molecular techniques. Antimicrobial resistance was assessed by the micro broth dilution. Toxins, flagella, and type III secretion system genes were evaluated by polymerase chain reaction. Biofilm was quantified by crystal-violet staining. Interaction with human intestinal epithelial cells (Caco-2) was assessed by quantifying adhesion, interleukin (IL)-8 secretion, and epithelial barrier integrity. Aeromonas spp. represented 20.6% of bacterial pathogens isolated from diarrheic feces, the second most common enteropathogen. A. cavieae constituted 75% of the identified species, showing a relatively low clustering value. About 52% of Aeromonas isolates showed resistance to amikacin, whereas only 7.5% showed multiple drug resistance. Four or more virulence genes were identified in 66.7% of A. cavieae isolates and 100% of A. dakensis. Aeromonas isolates (82.5%) showed moderate or important biofilm-producing ability. Adhesion to Caco-2 cells correlated to fla+ gene, whereas ascV+ and aexU+ strains significantly induced IL-8 release from Caco-2. Aeromonas aer+ strains caused ZO1 and occluding redistribution and a significative reduction in trans-epithelial resistance. Aeromonas spp. emerge as relevant human intestinal pathogens with a disparate arsenal of pathogenicity factors causing diarrhea through different mechanisms.