Table 1 In vitro MIC and FICI values for treatments against Gram-negative bacterial strains.

Species	FICI_polB/net Range	MIC_polB (A1)	Com_polB(A2)	MIC_polB/net Range	MIC_net (B1)	Com_net(B2)	MIC_net/polB Range
A. baumanii, clinical isolates (YCSAb5, 7) and colistin resitant clinical isolates (YCRAb49, 257, 269, 301, 615)
A. baumannii ATCC15150	0.25	2	0.25	0.001953–0.5	200	25	3.125–100
A. baumanii YCSAb5	0.375	1	0.25	0.125–0.25	200	25	3.2–100
A. baumanii YCSAb7	0.375	2	0.25	0.125–1	200	50	12.5–100
A. baumanii YCRAb49	0.75	16	8	8	800	200	200–400
A. baumanii YCRAb257	0.266	16	4	0.125–2	200	3.125	12.5–100
A. baumanii YCRAb269	0.508	8	4	0.25–2	400	3.125	3.125–100
A. baumanii YCRAb301	0.508	8	4	0.5–2	400	3.125	3.125–200
A. baumanii YCRAb615	0.508	8	4	0.125–2	400	3.125	3.125–200
Commensal and human pathogenic Gram-negative bacteria
E. coli MG1655	0.375	1	0.125	0.0625–0.125	50	12.5	0.098–25
S. flexneri SF2a	0.75	1	0.25	0.125–0.5	12.5	6.25	3.125–6.25
S. typhimurium LT2	0.625	4	0.5	0.250–0.5	25	12.5	6.25–12.5
P. aeruginosa PA14	1	1	0.5	0.5–1	400	200	400–200
P. aeruginosa YPa2	1.004	2	2	2	800	3.125	800

Abbreviations: Com, the most inhibitory concentration (MIC) value of combined antibiotics; FICI, fractional inhibitory concentration index; FICI_polB/net indicates the values at the most synergistic combination of polymyxin B and netropsin; MIC, minimum inhibitory concentration; net, netropsin; polB, polymyxin B; MIC_polB/net and MIC_net/polB represent the series of MIC values of polymyxin B or netropsin in the presence of netropsin or polymyxin B except the MIC values of monotherapy, respectively. FICI = MIC(A2)/MIC(A1) + MIC(B2)/MIC(B1). All MIC values are in mg/L.

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