Figure 1.

Vectors for the construction of a modified S1 gene into the allelic-exchange vector pSS4245. A: Allelic-exchange element for replacing the S1 gene by a chloramphenicol resistance cassette, inserted between the S1 flanging regions. B: Allelic-exchange element for returning the modified S1 gene into its exact location in the ptx-ptl operon. To obtain the allelic exchange, these vectors were linearized and inserted into pSS4245, which was then introduced into B. pertussis by conjugative transfer from E. coli SM10