TABLE 3.

In vitro activities of antimicrobial agents against E. coli and K. pneumoniae isolates that produce CTX-M and other types of ESBLs

Antimicrobialc	No. (%) of resistant isolatesa	MIC (μg/ml)b
		Range	50%	90%
E. coli, CTX-M (n = 28)
Ceftazidime	28 (100)	1-≥256	8	≥256
Cefotaxime	28 (100)	8-≥256	≥256	≥256
Cefepime	28 (100)	2-≥256	16	128
AMC	27 (96.4)	4-≥256	32	64
TZP	5 (17.9)	0.5-≥256	4	≥256
Imipenem	0	0.125-2	0.25	0.5
Gentamicin	25 (89.3)	1-≥256	64	≥256
Amikacin	0	1-8	2	4
Ciprofloxacin	6 (21.4)	0.004-≥32	0.03	≥32
E. coli, non-CTX-M (n = 50)
Ceftazidime	50 (100)	0.25-256	32	≥256
Cefotaxime	50 (100)	0.06-≥256	16	128
Cefepime	50 (100)	0.06-128	1	4
AMC	40 (80.0)	4-≥256	32	128
TZP	18 (36.0)	1-≥256	8	≥256
Imipenem	0	0.125-1	0.25	0.5
Gentamicin	38 (76.0)	0.5-≥256	32	≥256
Amikacin	8 (16.0)	0.5-≥256	2	≥256
Ciprofloxacin	25 (50.0)	0.008-≥256	1	≥32
K. pneumoniae, CTX-M (n = 87)
Ceftazidime	87 (100)	0.5-≥256	8	≥256
Cefotaxime	87 (100)	8-≥256	128	≥256
Cefepime	87 (100)	1-≥256	16	≥256
AMC	79 (90.8)	4-≥256	32	64
TZP	33 (37.9)	0.5-≥256	8	≥256
Imipenem	0	0.125-2	0.5	0.5
Gentamicin	83 (95.4)	1-≥256	128	≥256
Amikacin	17 (19.5)	1-64	2	32
Ciprofloxacin	16 (18.4)	0.016-≥32	0.06	8
K. pneumoniae, non-CTX-M (n = 161)
Ceftazidime	161 (100)	0.5-≥256	16	≥256
Cefotaxime	161 (100)	0.06-≥256	4	64
Cefepime	161 (100)	0.06-≥256	2	8
AMC	122 (75.8)	1-≥256	32	64
TZP	78 (48.4)	1-≥256	16	≥256
Imipenem	0	0.125-1	0.25	0.5
Gentamicin	128 (79.5)	0.5-≥256	32	≥256
Amikacin	20 (12.4)	1-≥256	2	32
Ciprofloxacin	38 (23.6)	0.032-≥32	0.125	4

^aRefers to cumulative number (percent) of isolates categorized as intermediate or resistant according to the NCCLS breakpoint criteria. All ESBL producers were considered resistant to ceftazidime, cefotaxime, and cefepime independent of MICs.

^b50% and 90%, MIC₅₀ and MIC₉₀, respectively.

^cAMC, amoxicillin-clavulanic acid (2:1). The concentrations listed refer to amoxicillin. TZP, piperacillin-tazobactam (tazobactam fixed at 4 μg/ml). The concentrations listed refer to piperacillin.