Table 1.

Minimum Inhibitory Concentrations (MICs) of polymyxin B and rifampicin potentiation against wild-type and polymyxin-resistant strains

		MIC (µM)a
Species	Background	Polymyxin B	PMBNb	Brevicidine
E. coli	WT	0.00008	>40	0.313
	PmrAG53E	10	>40	0.625
	mcr1c	2.5–5	>40	0.313
	WT+rifampicind	<0.00002	0.078	0.078
	PmrAG53E+rifampicind	0.001	20	0.078
	mcr-1+rifampicind	0.001	2.5	0.078
S. aureus	WT	>40	>40	>40

^aMinimal Inhibitory Concentrations (MICs): lowest concentration of antibiotic that completely inhibits bacterial growth.

^bPMBN, polymyxin B nonapeptide.

^cStrain carrying a plasmid encoding the mcr-1 gene.

^dRifampicin present at 1.56 µM, which has no effect on growth of E. coli or polymyxin-resistant E. coli strains tested.