Table 7.

Analysis of mutants selected on ciprofloxacin, 4 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		3.5 × 10−10	EFN + XY	8	<2 × 10−10
CIP76110		<2 × 10−10			2 × 10−10	EFN + T83I (GyrA)	8
BOU1		<2 × 10−10			<2 × 10−10
LAU1		<2 × 10−10			<2 × 10−10
MAR1		<2 × 10−10			<2 × 10−10
PUB1		<2 × 10−10			<2 × 10−10
SCL1		<2 × 10−10			<2 × 10−10
SCH1		<2 × 10−10			4 × 10−10	EFN + T83I (GyrA)	16
VIT1		<2 × 10−10			<2 × 10−10
Efflux overproducers (CIP MICs, 0.5 μg/ml)
32.1	ABM	<2 × 10−10			<2 × 10−10
37.1	ABM + XY	<2 × 10−10			2 × 10−10	T83I (GyrA)	16
40.1	EFN	<2 × 10−10			2 × 10−10	T83I (GyrA)	32
43.1	XY	1.8 × 10−9	EFN	8	2 × 10−10	T83I (GyrA)	8
3994	ABM + XY	2.3 × 10−9	EFN	8	<2 × 10−10
4016	XY	<2 × 10−10			1.8 × 10−9	T83I (GyrA)	16
4070	CDJ	<2 × 10−10			<2 × 10−10
4173	XY	<2 × 10−10			<2 × 10−10
4175	ABM	<2 × 10−10			<2 × 10−10
4177	EFN	9.3 × 10−10	Noc	8	<2 × 10−10

^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.

^cNo additional mechanism.