Construction of a bivalent oral vaccine for prevention of typhoid fever and cholera diarrhea.

A recombinant plasmid pMM-CTB containing the gene for production of the nontoxic B subunit of Vibrio cholera was transferred into a safe, effective and attenuated oral vaccine Ty21a strain of Salmonella typhi. The resulting Ty21a (pMM-CTB) could steadily produce CT-B subunit that was secreted extracellularly and had the same antigenicity as CT-B produced by V. cholera. Furthermore, the characteristics of the antigenicity, the persistance in mice and the galactose sensitivity possessed in the strain of Ty21a were also retained in Ty21a (pMM-CTB). A bivalent vaccine containing Ty21a (pMM-CTB) and the killed whole cell of V. cholera was then constructed which had good immunogenecity for typhoid fever and cholera diarrhea.