TABLE 2.

MICs of FOX, CTX, and CAZ in wild-type BW25113 E. coli and derivative isogenic Keio mutants carrying a CMY-2-encoding plasmid

Drug	MICa (μg/ml)
	Wild type	ΔmrcB	ΔdacA	ΔycfM	ΔybgF	ΔdapF	ΔdksA	ΔtolC	Susceptibility breakpoint	Resistance breakpoint
FOX	32	8	32	16	16	2	16	32	≤8	≥32
CTX	8	4	8	16	8	2	4	8	≤1	≥4
CAZ	32	8	32	32	32	32	16	32	≤4	≥16

^aMICs equal to or below the CLSI susceptibility breakpoints for Enterobacteriaceae (37) are indicated in boldface. The MICs of drugs for which individual gene deletion resulted in a synergistic effect (interaction index ≤ 0.25) are underlined.