Mechanisms of Resistance to Imipenem and Ampicillin in Enterococcus faecalis

DOI: 10.1128/AAC.49.7.2954-2958.2005

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FIG. 1.
Amino acid substitutions in pbp4 of E. faecalis strains. The homology boxes (STFK with active-site serine SDN and KTG) are indicated above. The positions at which resistant and low-resistant strains are altered from the sequence of the reference strain E. faecalis SEF96 are indicated.

TABLE 1.

Bacterial strains and MIC values of selected agents

Strain	Date of isolation (day.mo.yr)	Specimen and relevant characteristics	MIC (μg/ml)^a				Beta-lactamase produced
Strain	Date of isolation (day.mo.yr)	Specimen and relevant characteristics	AMP	IPM	CTX	VCM	Beta-lactamase produced
Enterococcus faecalis
SEF96	21.04.2000	Clinical isolate from urine	1	1	>256	1	−
ATCC 29212		Type strain	1	1	256	4	−
SVR 34	15.02.2000	Clinical isolate with vanB from urine	8	4	>256	32	−
SVR 138	27.05.2002	Clinical isolate with vanA from stool	8	8	>256	>512	−
SVR 250	19.07.2002	Clinical isolate with vanA from urine	1	0.5	64	>512	−
SVR 251	19.07.2002	Clinical isolate with vanA from urine	1	0.5	64	>512	−
SVR 1110	02.09.2000	Clinical isolate with vanA from urine	16	32	>256	>512	−
SVR 1119	01.12.1998	Clinical isolate with vanA from urine	16	32	>256	>512	−
SVR 1119S		ΔvanA; spontaneous mutant derived from SVR 1119	16	32	>256	1
Escherichia coli
ATCC 35218		Beta-lactamase-positive strain					+

↵a Abbreviations: AMP, ampicillin; IPM, imipenem; CTX, cefotaxime; VCM, vancomycin.

TABLE 2.

Primers designed for sequencing of PBP4 genes

Primer	Sequence	Reference
EF PBP4 140′F	5′CAACGAAAGCCTGATGAAATGG3′	This study
EF PBP4 1043F	5′CGATTGACAGTGTACAACAACAAGC3′	This study
EF PBP4 1132R	5′AATCGCCTTTTTGAGGATCGG3′	This study
EF PBP4 2130R	5′CGCTTCATTGTAGCACACTTTCCTTTTTC3′	4

TABLE 3.

Inhibition of binding of Bocillin FL to PBPs by two beta-lactams

Drug	E. faecalis strain	IC₅₀^a (μg/ml)				MIC (μg/ml)
Drug	E. faecalis strain	PBP1	PBP3	PBP4	PBP5	MIC (μg/ml)
Ampicillin	SEF96	1	0.5	0.25	>16	1
	ATCC 29212	1	0.5	0.25	>16	1
	SVR 250	2	0.5	1	>8	1
	SVR 251	2	0.5	0.25	>8	1
	SVR 34	2	0.5	4	>32	8
	SVR 138	2	0.5	4	>32	8
	SVR 1110	1	0.5	8	>32	16
	SVR 1119	1	0.25	8	>32	16
Imipenem	SEF96	0.5	0.25	0.25	>16	1
	ATCC 29212	0.5	0.25	0.125	>16	1
	SVR 250	1	0.5	0.25	>8	0.5
	SVR 251	0.5	0.25	0.5	>8	0.5
	SVR 34	0.5	0.25	4	>32	4
	SVR 138	0.5	0.25	4	>32	4
	SVR 1110	1	0.5	32	>32	32
	SVR 1119	1	0.25	16	>32	32

↵a IC₅₀, concentration of unlabeled antibiotic which reduces binding of Bocillin FL to a PBP by more than 50%.

TABLE 4.

Amino acid alterations in strains in this study compared with E. faecalis SEF96

Strain	MICs (μg/ml), ampicillin/imipenem	IC₅₀ (μg/ml), ampicillin/imipenem	Alteration at position:
Strain	MICs (μg/ml), ampicillin/imipenem	IC₅₀ (μg/ml), ampicillin/imipenem	50	369	520	605
SEF96	1/1	0.25/0.25	Tyr	Val	Pro	Tyr
ATCC 29212	1/1	0.25/0.125		Ala
SVR 250	1/0.5	1/0.25	Ile
SVR 251	1/0.5	0.25/0.5	Ile
SVR 34	8/4	4/4				His
SVR 138	8/4	4/4				His
SVR 1110	16/32	8/32			Ser	His
SVR 1119	16/32	8/32			Ser	His