Plasmid eller fagvektor som ikke inneholder en antibiotisk resistens determinant, Pur A-bakterievert som inneholder plasmidet eller vektoren,farmasöytiskpreparat som omfatter bakterien og fremgangsmåte for seleksjon ogopprettholdelse av bakte

摘要

This invention pertains to a complementation system for the selection and maintenance of expressed genes in bacterial hosts. The invention provides stable vectors which can be selected and maintained by complementation of chromosomal deletion mutations of purA (adenylosuccinate synthetase), obviating the use of antibiotic resistance genes. This system is useful in production organisms during fermentation and in live vaccine bacteria, such as attenuated Salmonella typhi. This system allows for selection of chromosomal integrants and for selection and stable plasmid maintenance in the vaccinated host without application of external selection pressure.