TABLE 1.

Antimicrobial susceptibilities, QRDR mutations, AcrA expression levels, and ciprofloxacin accumulation in clinical strains of K. pneumoniae and K. oxytoca

Strain	MIC (μg/ml)			QRDR mutation		AcrA expression levelb (mean ± SD)	Level of ciprofloxacin accumulationc with- out CCCP	With CCCP
	Ciprofloxacin	Nalidixic acid	Novobiocin	gyrA	parC
E. coli AG100a	0.03	4	256	None	None	1.0b	1.0c	1.0c
K. pneumoniae
KLPN 42	4	>512	256	S83Y	None	1.0 ± 0.047	0.83	0.95
KLPN 86	64	>512	>512	S83F	S80I	1.24 ± 0.051	0.42	1.08
KLPN 87	4	>512	16	S83Y	D79G	0.9 ± 0.07	0.85	1.1
KLPN 90	4	>512	128	S83Y	None	1.23 ± 0.03	0.55	1.1
KLPN 94	0.03	4	64	None	None	0.9 ± 0.15	1	1.1
KLPN 96	4	>512	128	S83Y	None	1.31 ± 0.11	0.55	1.0
KLPN 103	2	>512	64	S83Y	None	1.0 ± 0.045	0.42	0.87
KLPN 105	4	>512	64	None	None	1.7 ± 0.15	0.35	0.83
K. oxytoca
KLOXY 106	4	>512	256	T83I	None	2.2 ± 0.25	0.50	0.83
KLOXY 108	2	>512	256	T83I	None	2.2 ± 0.22	0.43	0.97
KLOXY 109	2	>512	256	T83I	None	1.65 ± 0.16	0.36	0.85
KLOXY 114	0.03	4	16	None	None	0.53 ± 0.1	1.20	1.36
KLOXY 116	4	>512	128	T83I	None	1.14 ± 0.03	0.73	0.96

^aWild-type strain that expresses a normal level of the AcrAB efflux system.

^bThe levels of expression of the AcrA protein were determined as described in the text and were expressed relative to that for E. coli AG100. Tests were repeated three times.

^cThe accumulation of ciprofloxacin (in nanograms per milligram of cells) was determined as described in the reference 9 and was expressed relative to that for E. coli AG100. CCCP was used at 100 μM.