Table 6.

Analysis of mutants selected on ciprofloxacin, 2 μg/ml^a

Strain	Background	Exponentially growing cells			Stationary-phase cells
		Mutation frequenciesb	Additional resistance mechanisms	CIP MIC (μg/ml)	Mutation frequenciesb	Additional resistance mechanisms	CIP MIC (μg/ml)
Wild-type strains (CIP MICs, 0.12 μg/ml)
PAO1		<2 × 10−10			<2 × 10−10
PA14		1 × 2.10−8	EFN	4	3.5 × 10−8	EFN	4
CIP76110		6.6 × 10−10	EFN	4	<2 × 10−10
BOU1		1.0 × 10−9	EFN	4	4.6 × 10−9	EFN	4
LAU1		9.3 × 10−9	EFN	4	4.0 × 10−10	EFN	8
MAR1		1.3 × 10−10	CDJ	4	<2 × 10−10
PUB1		1.2 × 10−9	Unknown	4	4.2 × 10−8	Unknown	8
SCL1		4.2 × 10−9	EFN	4	2.7 × 10−8	EFN	4
SCH1		1.6 × 10−9	EFN	4	4.2 × 10−9	EFN + T83I (GyrA)	16
			EFN + D87N (GyrA)	8
VIT1		1.6 × 10−9	EFN	4	8.0 × 10−10	EFN	4
Efflux overproducers (CIP MICs, 0.5 μg/ml)
32.1	ABM	3.3 × 10−10	EFN	4	4.0 × 10−10	EFN + D87Y (GyrA)	16
37.1	ABM + XY	2.6 × 10−9	EFN	4	4.0 × 10−10	EFN	4
40.1	EFN	1.3 × 10−10	T83I (GyrA)	8	6.0 × 10−10	S466Y (GyrB)	6
43.1	XY	1.2 × 10−9	EFN	4	4.8 × 10−9	T83I (GyrA)	8
3994	ABM + XY	1.7 × 10−8	CDJc	4	1.4 × 10−8	EFNc	4
			EFNc	4
4016	XY	3.4 × 10−9	CDJ	4	3.4 × 10−9	T83I (GyrA)	8
			ABM + D87Y (GyrA)	8
4070	CDJ	7.2 × 10−9	EFN	4	2.0 × 10−10	EFN	4
4173	XY	6.6 × 10−10	EFN	4	8.0 × 10−10	T83I (GyrA)	16
4175	ABM	<2 × 10−10			6.0 × 10−10	T83I (GyrA)	8
4177	EFN	1.1 × 10−8	Nod	4	3.9 × 10−9	Nod	4

^aCIP, ciprofloxacin; ABM, MexAB-OprM; CDJ, MexCD-OprJ; EFN, MexEF-OprN; XY, MexXY(OprM). Mutations in the QRDR regions are underlined.

^bCalculated from an initial inoculum of 5 × 10⁹ bacteria (experiments performed in triplicate). The value <2 × 10⁻¹⁰ indicates that no colonies were obtained on selective plates.

^cIn these mutants, the mexXY operon was no longer overexpressed.

^dNo additional mechanism.