Table 2.

Fold reduction in the MIC when comparing colistin alone vs. colistin with MSI-78 or colistin with OTD-244.

Species and CDC ID no.a	MSI-78 [μg/mL]	MIC colistin with MSI-78	Fold reductionc	OTD-244 [μg/mL]b	MIC colistin with OTD-244	Fold reductionc
Escherichia coli AR bank no. 0346	1.25	0.01	64	25	0.08	4
Escherichia coli AR bank no. 0349d	1.25	0.16	2	50	0.08	4
Escherichia coli AR bank no. 0350d	2	≤0.04	32	25	0.16	2
Escherichia coli AR bank no. 0493d	1.75	≤0.04	32	50	0.16	2
Escherichia coli AR bank no. 0494d	2	1.25	2	50	2.5	1
Escherichia coli AR bank no. 0495d	2	0.08	4	50	0.08	2
Escherichia coli AR bank no. 538d	1.75	0.04	16	50	1.25	1
Escherichia coli AR bank no. 0061	2	0.004	16	50	0.004	16
Escherichia coli AR bank no. 0089	2.5	0.03	4	50	0.01	8
Klebsiella pneumoniae AR bank no. 0497d	3.5	2.5	1	50	2.5	1
Klebsiella pneumoniae AR bank no. 0145	3.5	0.31	4	50	0.04	8
Acinetobacter baumannii AR bank no. 0035	1.25	0.016	1	50	0.001	16
Acinetobacter baumannii AR bank no. 0078	1.25	0.016	1	50	0.0005	16
Acinetobacter baumannii AR bank no. 0083	1.25	0.016	1	50	0.0005	64
Pseudomonas aeruginosa AR bank no. 0054	4.25	0.008	16	50	0.125	1
Pseudomonas aeruginosa AR bank no. 0353	3.0	0.031	4	50	0.125	1
Pseudomonas aeruginosa AR bank no. 0356	3.25	0.016	4	50	0.0625	1

^aSee Table 1 for isolate information; CDC, Centers for Disease Control and Prevention.

^bFixed concentration used for MSI-78 or OTD-244 was found by starting combination treatments with half the MIC (see Table 1).

^cValues in bold are considered a significant fold reduction. See Section 2.

^dIsolates positive for either mcr-1 or mcr-2.