Enterotoxicity and cytotoxicity of Vibrio parahaemolyticus thermostable direct hemolysin in in vitro systems

Vibrio parahaemolyticus is a marine bacterium known to be a common cause of seafood gastroenteritis worldwide. The thermostable direct hemolysin (TDH) has been proposed to be a major virulence factor of V. parahaemolyticus. T DH causes intestinal fluid secretion as web as cytotoxicity in a variety of cell types. In this study, we investigated the interplay between the hemol ysin's enterotoxic and cytotoxic effects by using both human and rat cell m onolayers, As revealed by microspectrofluorimetry, the toxin causes a dose- dependent increase in intracellular free calcium in both Caco-2 and IEC-6 c ells, This effect was reversible only when low toxin concentrations were te sted. The TDH-activated ion influx pathway is not selective for calcium but admits ions such sodium and manganese as well. Furthermore, in the same ra nge of concentration, the hemolysin triggers a calcium-dependent chloride s ecretion. At high concentrations, TDH induces a dose-dependent but calcium- independent cell death as assessed by functional, biochemical, and morpholo gical assays.