Characterization of virulence, cell surface characteristics and biofilm-forming ability of Aeromonas spp. isolates from fish and sea water.

Members of the genus Aeromonas are emerging human pathogens, causing a variety of extra-intestinal, systemic and gastrointestinal infections in both immunocompetent and immunocompromised persons. Aeromonas virulence is multifaceted and involves surface-associated molecules, motility, biologically active extracellular products and biofilm formation. Aeromonads, isolated from diverse freshwater fish species as well as sea water, were screened for biofilm formation, with varying physicochemical parameters including temperature, agitation and nutrient availability. Motility, cell surface characteristics (auto-aggregation, hydrophobicity and S layer), and extracellular virulence factor production (haemolysis, proteolysis, DNase production) were also assessed to identify potential associations with the biofilm phenotype. Biofilm formation was influenced by environmental conditions, with isolates preferentially forming biofilms in nutrient-rich media at 30 °C, although strong biofilm formation also occurred at 37 °C. Strong biofilm formation was observed for Aeromonas culicicola isolates following exposure to nutrient-rich conditions, while Aeromonas allosaccharophila isolates preferred nutrient-poor conditions for biofilm formation. Source-/species-specific correlations, ranging from weak to strong, were observed between biofilm formation and motility, cell surface characteristics and/or extracellular virulence factor production. Understanding the specific mechanisms by which Aeromonas species adhere to abiotic surfaces may aid in preventing and/or treating disease outbreaks in aquaculture systems and could lead to effective eradication of these fish pathogens.