TABLE 2.

MIC and FICI values against planktonic Staphylococcus aureus ATCC 6538 and Pseudomonas aeruginosa ATCC 27853^a

	PMB MICa (µg/mL)	PMB MICc (µg/mL)	P value (Mann-Whitney U)	EDTA MICa (mg/mL)	EDTA MICc (mg/mL)	P value (Mann-Whitney U)	FICI
S. aureus	256	64 (8–64)	0.002	4.2 (4.2–8.4)	1.2 (1.2–2.3)	0.002	0.5 (0.31–0.75)
P. aeruginosa	4	0.5	0.0009	67.5	9.4 (4.7–9.4)	0.001	0.39 (0.26–0.39)

^a All values are expressed as median (range). If there was no variation between replicates, no range is given. Where the median fell between two values, the higher of these values was recorded. PMB: polymyxin B. MIC_a: minimum inhibitory concentration of the antimicrobial when tested alone, recorded from MIC assays. MIC_c: minimum inhibitory concentration of the antimicrobial when tested in combination, recorded from checkerboard assays. FICI was calculated using MIC_a from the checkerboard assays except where the MIC_a determined in MIC assays was greater than that which could be tested on the checkerboard. Six technical replicates were performed per species.