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[A chromosomal integration system for development of polyvalent vaccine strains].

We have developed a potential bivalent vaccine stain through the chromosomal integration system in which the gene that codes for the B subunit of cholera toxin was integrated into the chromosome of an attenuated strain of Salmonella typhimurium. This system involves two steps: construction of a hisOG deletion mutation into the chromosome of S. typhimurium strain SL3261: and replacement of the hisOG deletion by the complete hisOG region and the segment of heterologous DNA which codes for the B subunit of cholera toxin. The recombinant strain SL3261 (named TT201) was obtained. Southern hybrid confirmed that the CTB gene was integrated into the chromosome of TT201. Western blot analysis demonstrated that the CTB gene was expressed stably in TT201. When administered orally to mice, the recombinant strain elicited a serum antibody response to CTB. The strain TT201 is a potentially bivalent vaccine candidate.