Interaction of Aeromonas strains with lactic acid bacteria using Caco-2 cells

The genus Aeromonas includes some species that have now been identified as a human pathogen of significant medical importance. We investigated the ability of 13 selected Aeromonas strains belonging to nine species isolated from clinical cases (n=5), environmental waters (n=5) and fish (n=3) to adhere to and translocate Caco-2 cells in the absence and presence of two lactic acid bacteria (LAB) i.e. Lactobacillus acidophilus and Bifidobacterium breve. Aeromonas isolates were also assessed for their cytotoxicity, presence of virulence genes and hemolysin production. Among the clinical isolates one strain of A. veronii biovar veronii and two strains of A. hydrophila carried cytotoxin (act), heat-labile toxin (alt), hemolysin (hlyA) and aerolysin (aerA) genes, were cytotoxic to Vero cells, produced hemolysin and showed higher adherence to Caco-2 cells. In contrast this was only seen in one environmental strain of A. veronii biovar sobria. When Aeromonas strains were co-inoculated with LAB onto Caco-2 cells, their level of adhesion reduced. However, their rate of translocation in the presence of LAB increased and this was significantly (p less than 0.05) higher amongst fish strains. We suggest that the interaction between Aeromonas and LAB strains could either have a detrimental effect on the Caco-2 cells, allowing the Aeromonas to translocate more readily, or that the presence of the LAB stimulated the Aeromonas strains to produce more toxins and/or increase their translocation rate