Characterization of the Outermembrane Proteins of Vibrio cholerae Expressed in In Vivo Culture

Two outer membrane proteins (Omps) of Vibrio cholerae O1, expressed in the intestine (in vivo) but not in culture media (in vitro), were investigated. The molecular masses of those proteins were 116 kDa and 15 kDa, and they were not associated with iron‐regulated proteins. Convalescent cholera patients' sera reacted with the 15 kDa protein but not with the 116 kDa protein. The N‐terminal amino acid sequence of the 15 kDa protein was homologous to V. cholerae OmpT. Anti‐serum to the 15 kDa protein caused agglutination of the organisms grown in the intestine, but not the organisms in in vitro culture. The antiserum was bactericidal, but it did not inhibit the adhesion of the organisms to the intestine and HEp‐2 cells. These findings suggest the possibility that the 15 kDa protein could be involved in post‐infection immunity.