FIG 2.

Most core PBr genes confer resistance through loss of function. Polymyxin B resistance of deletion or insertional disruption mutants (A) and selected mutants transformed with plasmids expressing GdpP (pGdpP), ClpX (pClpX), or empty pABG5 vector (Vector) (B) was determined by efficiency of plating on solid medium. Stationary-phase cultures of indicated strains were serially diluted and plated onto solidified C medium either unmodified or containing 40 μg ml⁻¹ polymyxin B. Efficiency of plating was calculated as log₁₀ CFU_+PB/log₁₀ CFU_unmod. Data shown are the means and the standard errors of the means derived from at least four independent experiments. Differences between wild-type and mutant strains were tested for significance using the Dunnett test (*, P < 0.01).