TABLE 2.

Antimicrobial susceptibilities to β-lactam antibiotics for 118 KPC- and ESBL-producing isolates and 37 KPC-producing non-ESBL-producing isolates

Strain group and antimicrobial	MIC (μg/ml)			% Resistanta
	Range	50%	90%
ESBL-producing isolates
Aztreonam	128->256	256	>256	100
Cefepime	16-128	64	128	85.6
CTX	64->128	64	>128	100
CAZ	128->256	128	>256	100
Ertapenem	4-64	16	32	90.7
Imipenem	4-64	16	32	66.1
Meropenem	2-64	16	32	61.9
Piperacillin-tazobactam	256->256	256	>256	100
Non-ESBL-producing isolates
Aztreonam	64->256	128	256	100
Cefepime	8-128	16	128	43.2
CTX	16-128	64	128	73.0
CAZ	8-128	32	128	70.3
Ertapenem	4-64	8	32	54.0
Imipenem	2-32	8	16	43.2
Meropenem	2-32	8	16	37.8
Piperacillin-tazobactam	16->256	128	256	81.1

^aThe CLSI breakpoints used to define resistance were as follows: aztreonam, ≥32 μg/ml; ertapenem, ≥8 μg/ml; cefepime, ≥32 μg/ml; CTX, ≥64 μg/ml; CAZ, ≥32 μg/ml; imipenem, ≥16 μg/ml; meropenem, ≥16 μg/ml; piperacillin-tazobactam, ≥128/4 μg/ml.