(A) Western blot analysis of wild-type and ΔbrkA strains of B. pertussis. Phage transduction was performed to transfer the ΔbrkA mutation from RFBP2152 into several strains of B. pertussis. Western blot analysis was used to confirm successful transductants, verifying the presence of the 73-kDa processed BrkA protein in wild-type strains BP338, Tohama I, 6068, and GMT1 and its absence in their respective mutants, RFBP2125, BP338ΔbrkA, TohΔbrkA, 6068ΔbrkA, and GMT1ΔbrkA. (B) Colonization by wild-type and ΔbrkA mutants of B. pertussis at 3 days postinoculation. Groups of three 4-to 6-week-old C57BL/6 mice were inoculated with 5 × 105 CFU of BP338, RFBP2152, BP338ΔbrkA, Tohama I, TohΔbrkA, 6068, 6068ΔbrkA, GMT1, or GMT1ΔbrkA delivered in a 50-μl volume of PBS into the nares. The number of bacteria recovered from the lungs at 3 days postinoculation is expressed as the log10 mean ± the standard error. Key statistical differences between groups are indicated (*, P < 0.05). Dashed line indicates limit of detection.