TABLE 4.

IC₅₀ and K_i of β-lactamase inhibitors^a

Enzyme	Clavulanic acid		Tazobactam		Sulbactam
	IC50 (nM)	Ki (nM)	IC50 (nM)	Ki (nM)	IC50 (nM)	Ki (nM)
CTX-M-15	23.2	5.40 ± 1.24	7.61	0.92 ± 0.37	50.4	6.23 ± 2.51
CTX-M-55	13.9	2.37 ± 0.80	6.88	0.86 ± 0.15	50.7	7.59 ± 1.17
CTX-M-132	16.7	4.60 ± 0.51	3.70	1.07 ± 0.16	30.8	17.3 ± 1.73
CTX-M-123	17.6	3.37 ± 0.34	1.72	0.52 ± 0.11	59.4	11.1 ± 1.55
CTX-M-64	22.3	5.87 ± 1.28	5.75	1.44 ± 0.22	45.4	14.9 ± 1.79
CTX-M-14	60.1	24.3 ± 2.40	7.28	1.62 ± 0.25	403	119 ± 31.3

^aThe IC₅₀ and K_i values in the competition experiments were calculated using nitrocefin as the reporter substrate.