TABLE 1.

Amino acid alterations of CTX-M-190 and IC₅₀s of tazobactam, sulbactam, and clavulanate for CTX-M-15, CTX-M-55, and CTX-M-190

β-Lactamase	Amino acid alteration (vs CTX-M-1 sequence) at position:					Mean IC50 ± SD (μM)a
	80	117	133	242	289	Tazobactam	Sulbactam	Clavulanate
CTX-M-1	Val	Asp	Ser	Asp	Asn	NDb	ND	ND
CTX-M-3	Ala	Asn			Asp	ND	ND	ND
CTX-M-15	Ala	Asn		Gly	Asp	1.5 ± 0.4	5.8 ± 1.7	3.4 ± 0.7
CTX-M-55		Asn		Gly	Asp	0.6 ± 0.2	1.4 ± 0.6	0.8 ± 0.3
CTX-M-190		Asn	Thr	Gly	Asp	46.2 ± 4.8	77.3 ± 5.2	0.5 ± 0.2

^aIC₅₀, concentration of the β-lactamase inhibitor required to attain 50% enzyme inhibition. Data are the averages of the results obtained from three independent experiments.

^bNot determined.