Table 4

MICs to polymyxins of the wild-type H103, the cprR and cprS mutants, and their respective cprR+ and cprS+ complemented strains under different conditionsa

AntibioticMIC (μg/ml)
WTcprRcprScprR+cprS+
In minimal medium with high (2 mM) Mg2+
    Polymyxin B11111
    Colistin11111
In minimal medium with high (2 mM) Mg2+ supplemented with 4 μg/ml indolicidinb
    Polymyxin Bb80.50.51–28
    Colistinb>80.50.52–4>8
In minimal medium with low (20 μM) Mg2+
    Polymyxin B168888
    Colistin3232163232
  • a MICs were determined by serial 2-fold dilutions in BM2-glucose minimal medium with 2 mM Mg2+, unless indicated otherwise. The MIC represents the concentration at which no growth was observed after 24 h of incubation at 37°C. The values shown are the modes of 4 to 8 independent experiments.

  • b The cultures used to inoculate the MIC plates were also grown in the presence of indolicidin.