TABLE 1.

Effects of amino acid substitutions in regulator MexT

Strain	MexT substitution (304 aaa)	Transcript levelb			MIC (μg · ml−1)c						Reference or source
		mexEd	oprD	mexB	CIP	CHL	TMP	IMP	MEM	ATM
Clinical strains
4177	R166H	20	NDe	0.6	0.5	1,024	1,024	16	2	32	6
4088	G257S	112	ND	0.4	1	2,048	>2,048	8	0,25	1	6
10-12	G257A	26	NRf	9.2	2	128	>2,048	16	ND	32	8
0810	G258D	32	ND	ND	8	1,024	1,024	4	1	ND	7
1510	Y138D plus G258D	21	ND	ND	2	256	512	16	8	ND	7
Complemented PA14 derivatives
PA14	WTg	1	1	1	0.125	64	64	1	0.5	4	F. Ausubel
PA14ΔmexS	WT	192 ± 9.2	0.3 ± 0.1	0.4 ± 0.2	2	2,048	>2,048	4	2	2	7
PA14ΔmexT	−h	0.4 ± 0.1	1.7 ± 0.2	2.2 ± 0.2	0.125	32	32	1	0.5	4	This study
PA14ΔmexTPA14	WT	2.2 ± 0.7	1.1 ± 0.1	1.4 ± 0.2	0.125	64	64	1	0.5	4	This study
PA14ΔmexT4177	R166H	3.2 ± 0.3	2.0 ± 0.2	2.6 ± 0.1	0.125	64	64	1	0.5	4	This study
PA14ΔmexT4088	G257S	189 ± 5.9	0.4 ± 0.1	0.9 ± 0.1	2	2,048	>2,048	2	1	2	This study
PA14ΔmexT10-12	G257A	110 ± 3.6	0.4 ± 0.1	0.9 ± 0.1	1	1,024	1,024	2	1	2	This study
PA14ΔmexT0810	G258D	1.9 ± 0.4	0.9 ± 0.1	1.4 ± 0.1	0.125	64	64	1	0.5	4	This study
PA14ΔmexT1510	Y138D plus G258D	6.3 ± 0.2	0.9 ± 0.1	1.4 ± 0.1	0.25	64	64	1	0.5	4	This study

^aaa, amino acids.

^bMean gene expression values were calculated from two independent bacterial cultures, each of which was assayed in duplicates. They are expressed as a ratio to the gene transcription level in wild-type reference strain PA14.

^cCIP (ciprofloxacin), CHL (chloramphenicol), and TMP (trimethoprim) are substrates of MexEF-OprN. IMP (imipenem) and MEM (meropenem) are substrates of porin OprD (corepressed with mexEF-oprN overexpression). ATM (aztreonam) is a substrate of MexAB-OprM.

^dSignificant overexpression of mexE (threshold fixed at 20-fold) and increase in resistance to MexEF-OprN substrates is indicated in boldface type.

^eND, not determined.

^fNR, not relevant because of a codon stop in the oprD gene.

^gWT, wild type.

^h−, deleted gene.