TABLE 1.

Gram-negative rod-shaped bacterial strains used in this study, their MICs for colistin, heteroresistance, mutation frequency, and amino acid alterations in colistin-resistant mutants and colistin-susceptible revertants

Species	Strain	ST	Colistin MIC (μg/ml) for:			Heteroresistancea	Mutation frequencyb	Amino acid alteration in:
			Parent	Resistant mutant	Susceptible revertant			Colistin-resistant mutants				Colistin-susceptible revertantsc
								PmrA	PmrB	PhoP	PhoQ
A. baumannii	H07-988	220	1	>64		HR	8.69 × 10−7		H263R, V444A			NA
	H05-513	20	1	>64	1	HR	5.58 × 10−6		I235T, G390V			T235I, V390G in PmrB
	H09-673	92	1	>64			6.64 × 10−7		H263R			NA
	H09-968	138	1	>64			1.84 × 10−7	M12R				NA
	C095	110	0.5	>64			2.72 × 10−7					NA
P. aeruginosa	P5	235	1	>64	1		5.74 × 10−6				K123Q V260G	R117L in PhoP, Q123K in PhoQ
	P6	1340	2	64	0.5	HR	8.29 × 10−7		A67T			T67A in PmrB
	P33	641	1	>64			4.81 × 10−7		V15I			NA
	P155	17	0.5	>64	0.5	HR	3.41 × 10−6		L167P			P167L in PmrB, A110V in PhoP, Q411* in PhoQ
K. pneumoniae	B0608-134	730	1	>64		HR	2.94 × 10−6					NA
	B0704-039	11	0.5	>64		HR	4.28 × 10−6					NA
	08-B063	23	0.5	>64		HR	2.94 × 10−6				Y268S, del14–18	NA
	B0701-068	152	0.5	>64		HR	2.16 × 10−6					NA
E. coli	E015	405	0.25	64	0.25	HR	3.23 × 10−7		del133–136			V24E and del162–165 in PmrB
	E139	131	0.25	>64			4.23 × 10−7		P94L			NA
	E154	38	0.25	64			8.06 × 10−8		A159V			NA
	E188	410	0.125	64			1.03 × 10−7		V125E			NA

^aHeteroresistance (HR) was defined as the presence of colonies more than the LOQ on the agar plate containing 10 μg/ml colistin.

^bThe ratio of the CFU on a plate containing 4 μg/ml colistin to that on an antibiotic-free plate.

^cNA, not available; *, premature termination.