TABLE 1.

The MICs of different β-lactam antibiotics against E. coli JM83 producing wild-type and variant GES β-lactamases

Enzyme	MIC
	Ampicillin	Penicillin G	Cephalothin	Imipenem
	μg/ml
GES-1 (wt)	2048	1024	1024	0.25
C69G	1024	1024	128	0.25
C69A	4	16	8	0.25
C69L	4	16	8	0.25
C69M	4	16	8	0.25
GES-2 (wt)	2048	1024	512	0.25
C69G	1024	256	512	0.25
C69A	4	16	8	0.25
C69L	4	16	8	0.25
C69M	4	16	8	0.25
GES-5 (wt)	2048 (2048)a	1024 (1024)	1024 (1024)	1 (1)
C69G	512 (1024)	256 (512)	64 (128)	0.25 (0.5)
C69A	4 (4)	16 (16)	8 (8)	0.25 (0.25)
C69L	4 (4)	16 (16)	8 (8)	0.25 (0.25)
C69M	4 (4)	16 (16)	8 (8)	0.25 (0.25)
Controlb	4 (4)	16 (16)	8 (8)	0.25 (0.25)

^a MIC values given in parentheses were determined at 30 °C

^b Parental E. coli JM83 strain with pHF016 vector (no β-lactamase gene).