Association of cholera toxin with Vibrio cholerae outer membrane vesicles which are internalized by human intestinal epithelial cells

Cholera toxin (CT) is the major virulence factor of pathogenic Vibrio cholerae. The present study demonstrates that a fraction of CT is associated with the outer membrane vesicles (OMVs) released by V. cholerae. Atomic force microscopy (AFM) and also transmission electron microscopy (TEM) of purified OMVs from toxigenic V. cholerae O395 revealed spherical shaped vesicles of size range 20-200 nm. Immunoblotting of purified OMVs with polyclonal anti-CT antibody and GM1-ganglioside dependent ELISA suggest that CT is associated with OMVs. CHO cell assay indicated that OMV associated CT is physiologically active. OMVs labeled with fluorescent dye interacted with intestinal epithelial cells via the CT-receptor and were internalized increasing the cAMP level. Thus OMVs may represent an important vehicle in delivering CT to epithelial cells.