Recombinant Bordetella pertussis strains derived from parent strain Tohama are provided. The new strains are obtained by homologous recombination using a allelic exchange vector pSS4245, which allows the replacement of sections of the bacterial chromosome without leaving any accessory mutations. The segment encoding PT subunit S1 is replaced to introduce two mutations causing inactivation of the toxic activity of PT. This strain can be further modified to express increased amounts of rPT and/or PRN. A second copy of the ptx cluster of the five PT structural genes of the ptx-ptl operon with their promoter and the ptl terminator and containing the above mutations can be inserted elsewhere on the chromosome. In addition, a second copy of the PRN gene can be inserted on the chromosome. In both cases, abandoned gene loci are selected as the insertion site to avoid the introduction of unwanted genetic alterations.
