TABLE 3.

MBC and FBCI values against planktonic Staphylococcus aureus ATCC 6538 and Pseudomonas aeruginosa ATCC 27853^a

	PMB MBCa (µg/mL)	PMB MBCc (µg/mL)	P value (Mann-Whitney U)	EDTA MBCa (mg/mL)	EDTA MBCc (mg/mL)	P value (Mann-Whitney U)	FBCI
S. aureus	512 (512–2,048)	256 (8–256)	0.003	16.9	4.7 (0.6–9.4)	0.002	0.56 (0.52–1.0)
P. aeruginosa	4	1 (0.5–2)	0.002	67.5	9.4 (0.6–18.8)	0.002	0.39 (0.32–0.53)

^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 reported. PMB: polymyxin B. MBC_a: minimum bactericidal concentration of the antimicrobial when tested alone, reported from MBC assays. MBC_c: minimum bactericidal concentration of the antimicrobial when tested in combination, reported from checkerboard assays. FBCI was calculated using MBC_a from the checkerboard assays except where the MBC_a determined in MBC assays was greater than that which could be tested on the checkerboard. Six technical replicates were performed per species.