TABLE 4.

MICs of various beta-lactam antibiotics alone and in combination with QPX7728 against isogenic strains of P. aeruginosa overexpressing MexAB-OprM and/or chromosomal AmpC^a

Strain	MexAB-OprM	AmpCb	MIC (μg/ml)
			Meropenem			Ceftolozane			Cefepime			Ceftazidime			Piperacillin
			Alone	With QPX7728 at:		Alone	With QPX7728 at:		Alone	With QPX7728 at:		Alone	With QPX7728 at:		Alone	With QPX7728 at:
				4 μg/ml	8 μg/ml		4 μg/ml	8 μg/ml		4 μg/ml	8 μg/ml		4 μg/ml	8 μg/ml		4 μg/ml	8 μg/ml
PAM1020	BL	1	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5	1	1	1	4	4	4
PAM2156	BL	489	2	0.5	0.5	4	0.5	0.5	8	0.5	0.5	32	1	1	>256	16	4
PAM1032	Up	0.8	2	2	2	0.5	0.5	0.5	4	4	4	4	4	4	16	16	16
PAM2005	Up	769	4	2	2	4	1	0.5	16	4	4	64	8	8	>256	128	32

^aQPX7728 was used at a fixed concentration of 8 μg/ml. All strains are derivatives of PAM1020 (PAO1). BL, basal level; Up, overexpressed. Overexpression of the MexAB-OprM efflux pump in PAM1032 and PAM2005 is due to the L75R amino acid substitution in the MexR protein. PAM2005 was selected from PAM1032 on piperacillin at 64 μg/ml. It has AmpC overproduced due to the D135H amino acid substitution in the AmpR protein. PAM2156 was obtained by transducing a piperacillin resistance marker from PAM1032 into PAM1020 using phage F116, as described in Materials and Methods. The QPX7728 MIC against all strains was >128 μg/ml.

^bThe numbers correspond to the level of expression of the chromosomal ampC relative to that in PAM1020.