Caspase-3 Activation and Apoptosis Induction in THP-1 Human Monocytic Cells by Clinical and Environmental Isolates of Vibrio vulnificus

Vibrio vulnificus is an estuarine bacterium that is severely invasive and fatal for susceptible persons. The pathogenesis of V. vulnificus has not yet been clarified. This study showed that clinical strains as well as freshly-isolated environmental strains-but not storedenvironmental strains-of V. vulnificus markedly activated caspase proteolytic activities, such as caspase-3, -2, and -6 of THP-1 human monocytic cells. Caspase-3 activation was correlated with internucleosomal DNA fragmentation and chromation condensation of the cells. V. vulnificus activities responsible for the caspase-3 activation were present in the culture filtrates and were temperature-resistant. Consistent with the caspase-3 activation levels, the clinical strains and freshly-isolated environmental strains exhibited strong lethality in mice as compared with storedenvironmental strains. These data suggest that the caspase-3 activation factor could be a major factor in virulence produced by V. vulnificus.