. 2006 Aug;50(8):2700–2706. doi: 10.1128/AAC.00068-06

TABLE 4.

MICs of cefotaxime and ceftazidime and inhibitory-zone diameters of expanded-spectrum cephalosporins and aztreonam for CTX-M-producing isolates

Species	Enzyme (no. of isolates)	MIC (μg/ml)^a						Inhibitory zone diam (mm)^a^,^b
		CTX			CAZ			CTX		CAZ		ATM		FEP range
		Range	Median	MIC₉₀	Range	Median	MIC₉₀	Range	% Id^d	Range	% Id	Range	% Id	FEP range
E. coli	CTX-M-1 (35)	32->256	64	> 256	2-8	2	4	6-14	100	16-24	82	10-18	100	14-22
	CTX-M-15 (64)	64->256	256	> 256	4->256	32	128	6-14	100	6-20	100	6-18	100	10-22
	CTX-M-32 (4)	128->256	256		16-48	32		6-10	100	14-16	100	6-12	100	16
K. pneumoniae	CTX-M-1 (3)	24->256			32-64			6-10	100	14-20	100	6-14	100	10-18
	CTX-M-15 (5)	64->256	128		24-64	32		6-10	100	10-14	100	6-10	100	10-20
	CTX-M-32 (2)	>256			>256			6	100	6	100	6	100	14-16

CTX, cefotaxime; CAZ, ceftaxidime.

ATM, aztreonam; FEP, cefepime.

A 6-mm value means no zone of inhibition. The breakpoints for suspicion of ESBL production were as follows: CTX, ≤27 mm; CAZ, ≤22 mm; ATM, ≤27 mm (10).

% Id, percentage of isolates categorized as putative ESBL producers by disk diffusion testing, based on the CLSI breakpoint for suspicion of ESBL production, with the corresponding drug (10).