Figure 3

Effects of K. pneumoniae pmrA, pmrD and phoP deletion and complementation in polymyxin B resistance and intramacrophage survival. (A) The log-phased cultures of K. pneumoniae CG43S3, the ΔpmrA, ΔpmrD or ΔphoP mutants were grown in LB, LB supplemented with 10 mM Mg²⁺ or LB supplemented with 1 mM Fe³⁺ and then challenged with 2 units/ml of polymyxin B. The survival rates are shown as the average ± standard deviations from triplicate samples. (B) The log-phased cultures of K. pneumoniae CG43S3 carrying pRK415, the ΔpmrA ΔphoP mutant strains carrying pRK415, pRK415-PhoP or pRK415-PmrA were grown in LB and challenged with 2 units/ml of polymyxin B. The survival rates are shown as the average ± standard deviations from triplicate samples. (C) The survival rates of K. pneumoniae CG43S3ΔrcsB, the isogenic ΔpmrA ΔrcsB, ΔphoP ΔrcsB and ΔpmrD ΔrcsB mutants, and each mutant strain carrying the complementation plasmids pRK415-PmrA, pRK415-PhoP or pRK415-PmrD within the mouse macrophage RAW264.7 were determined. The results shown are relative survival rates which were calculated from the viable colony counts of intracellular bacteria divided by individual original inoculums. Values are shown as the average of five replicas. Error bars, standard deviations. *, P < 0.01 compared to each parental strain; **, P < 0.01 compared to each mutant strain carrying the complementation plasmid.