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 conditions^a

Antibiotic	MIC (μg/ml)
	WT	cprR	cprS	cprR+	cprS+
In minimal medium with high (2 mM) Mg2+
Polymyxin B	1	1	1	1	1
Colistin	1	1	1	1	1
In minimal medium with high (2 mM) Mg2+ supplemented with 4 μg/ml indolicidinb
Polymyxin Bb	8	0.5	0.5	1–2	8
Colistinb	>8	0.5	0.5	2–4	>8
In minimal medium with low (20 μM) Mg2+
Polymyxin B	16	8	8	8	8
Colistin	32	32	16	32	32

^aMICs 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.

^bThe cultures used to inoculate the MIC plates were also grown in the presence of indolicidin.