Aeromonas spp. induce apoptosis of epithelial cells through an oxidant-dependent activation of the mitochondrial pathway.

We investigated interactions of Aeromonas caviae, Aeromonas veronii biotype sobria and Aeromonas hydrophila strains, isolated from faecal specimens of humans with gastroenteritis, with HT29 intestinal epithelial cells. All strains were found to be cytotoxic to the cells. Bacterial infection caused generation of reactive oxygen species (ROS) and nitric oxide radical (NO(·)). The maximal levels of ROS and NO(·) were 14 and 35 times, respectively, greater in cells infected with Aeromonas spp. than in those incubated with non-pathogenic Escherichia coli. The cells incubated with cytolytic enterotoxin isolated from A. veronii biotype sobria induced the highest level of ROS and caused the highest cytotoxicity. We observed that increased accumulation of intracellular ROS leads to a loss of mitochondrial membrane potential (ΔΨ(m)). Analyses of cellular morphology and DNA fragmentation revealed characteristic features of cells undergoing apoptosis. The process was dependent on the activation of caspases, and was completely blocked by the pan-caspase inhibitor z-VAD-fmk. Treatment of infected HT29 cells with three distinct antioxidants prevented intracellular ROS production, mitochondrial damage and apoptosis. The Pearson linear test revealed positive correlations between apoptotic index at 24 h and percentage cytotoxicity, ROS production, NO(·) production and loss of ΔΨ(m). This study has provided new insights into the mechanisms contributing to the development of Aeromonas-associated gastroenteritis. The results indicate that bacteria-induced apoptosis of epithelial cells results from mitochondrial depolarization due to oxidative stress.