Figure 2. Colony PCR screening for pXO1 elimination with three plasmid-specific primer pairs.

Results of using recombinant plasmids pKS11K (A), pKS4K (B), and pKS5K (C) to eliminate the large plasmid pXO1 from B. anthracis vaccine strain A16R by plasmid incompatibility. The presence of anthrax toxin genes pagA, lef, and cya was determined by PCR analysis of the vaccine strain A16R (1) and the putative pXO1-cured strain A16R (2). M, DNA marker IV (Real-Times Biotechnology, Beijing, China).