TABLE 1.

Strains used in this work, displayed with their features related to the profile of β-lactam resistance (ceftazidime MIC and ampC expression)

Strain	Genotype/relevant characteristic(s)	Ceftazidime MIC (mg/liter)	ampC mRNA expression, mean ± SDa	Source or reference
PAO1b	Completely sequenced reference strain	1	1	Laboratory collection
PAΔD	PAO1 ΔampD::lox; AmpD is an N-acetyl-anhydromuramyl-l-alanine amidase involved in peptidoglycan recycling; negative regulator of AmpC expression	8	47 ± 9.5	56
PAΔDh2	PAO1 ΔampDh2::lox; AmpDh2 is an additional AmpD homologue of P. aeruginosa	0.75	1.1 ± 0.2	56
PAΔDh3	PAO1 ΔampDh3::lox; AmpDh3 is an additional AmpD homologue of P. aeruginosa	1	1.2 ± 0.3	56
PAΔDh2Dh3	PAO1 ΔampDh2::lox ΔampDh3::lox	0.75	2.3 ± 0.14	56
PAΔDDh2	PAO1 ΔampD::lox ΔampDh2::lox	12	79.5 ± 12.2	56
PAΔDDh3	PAO1 ΔampD::lox ΔampDh3::lox	48	251.2 ± 51.9	56
PAΔDDh2Dh3	PAO1 ΔampD::lox ΔampDh2::lox ΔampDh3::lox; mutant derepressed for AmpC production	48	1,225 ± 101	56
PAΔdB	PAO1 ΔdacB::lox; dacB encodes the nonessential penicillin-binding protein 4	24	51 ± 16	57
PAdacBΔD	1A1 spontaneous dacB knockout mutant (W273X) of PAO1; ampD::lox; mutant derepressed for AmpC production	96	1,770 ± 401	57
PAΔAG	PAO1 ΔampG::lox; ampG encodes the specific permease allowing the entry of certain muropeptides into the cytosol	1	1.1 ± 0.4	47
PAΔDDh2Dh3ΔAG	PAO1 ΔampD::lox ΔampDh2::lox ΔampDh3::lox ΔampG::lox	1	0.95 ± 0.2	74
PAdacBΔDG	1A1 spontaneous dacB knockout mutant (W273X) of PAO1; ampD::lox ampG::lox	0.75	1.7 ± 0.6	47

^aData obtained from the indicated references.

^bThe ampC mRNA level in PAO1 under cefoxitin induction was 50 ± 14 with regard to basal conditions.