Role of Hlya-positive Vibrio Cholerae Non-o1/non-o139 on Apoptosis and Cytotoxicity in a Chinese Hamster Ovary Cell Line.

Vibrio cholerae non-O1/non-O139 is capable of producing sporadic outbreaks of cholera-like diarrhea; however, the pathogenic mechanisms of this bacterium remain unclear. The objectives of this study were to: 1) compare the apoptosis induction and cytotoxicity between hlyA-positive and hlyA-negative strains of V. cholerae non-O1/non-O139; 2) clarify the molecular mechanisms by which these strains induce apoptosis; and 3) compare clinical and environmental V. cholerae non-O1/non-O139 isolates with respect to cytotoxicity and ability to induce apoptosis. Using cytotoxicity and apoptosis assays, it was shown that hlyA-positive strains of V. cholerae non-O1/non-O139 had significantly higher cytotoxic activity (70.6%) and levels of apoptosis induction (59.6%) than hlyA- negative strains (37.0% and 37.5%, respectively). Western blot analyses revealed that hlyA-positive strains had significantly increased expression of Bax; active caspase-3 and -9; and significantly decreased expression of NF-κB and Bcl-2 relative to hlyA-negative strains. Expression of BID did not differ significantly between hlyA-positive and negative strains. The truncated BID was not found, indicating that V. cholerae non-O1/non-O139 induces apoptosis through a mitochondria- dependent apoptosis pathway and not an extrinsic pathway. V. cholerae non-O1/ non-O139 isolated from clinical sources exhibited significantly higher cytotoxic activity (79%) and levels of apoptosis induction (65.2%) than bacteria isolated from environmental sources (63% and 54.6%, respectively), suggesting that the clini- cal isolates may have other virulence-associated genes besides hlyA. Our results indicate that hlyA products play a role in cytotoxicity and apoptosis induction and that a mitochondria-dependent apoptosis pathway is involved.