TABLE 2.

In vitro activities and MIC distributions of five different antibiotics tested against ampicillin-, SXT-, and ciprofloxacin-resistant isolates of E. coli

E. coli isolate group (n) and antibiotic	MIC50 (μg/ml)	MIC90 (μg/ml)	Range (μg/ml)	% Resistanta	No. of isolates inhibited by MIC (μg/ml) of:
					≤0.03	0.06	0.12	0.25	0.5	1	2	4	8	16	32	64	128	256	512	>512
Ampicillin-resistant (689)
Ampicillin	512	>512	32–>512	100					0	0	0	0	0	0	11	18	46	190	204	220
Ciprofloxacin	≤0.03	≤0.03	≤0.03–32	2.0	643	9	3	6	0	14	0	0	5	2	7
Mecillinam	4	64	≤0.5–>512	14.8					75	75	35	287	115	27	5	12	19	9	21	9
Nitrofurantoin	16	16	4–128	0.2							0	9	149	473	48	9	1	0	0	0
SXT	0.5	>64	≤0.06–128	35.7		155	71	79	100	26	12	6	5	0	8	4	223
SXT-resistant (317)
Ampicillin	256	>512	2–>512	79.6					0	0	26	18	20	0	0	5	18	74	69	86
Ciprofloxacin	≤0.03	0.25	≤0.03–32	6.3	282	0	3	3	0	9	0	1	3	7	9
Mecillinam	4	64	≤0.5–>512	15.1					82	36	27	83	41	10	0	7	8	8	7	8
Nitrofurantoin	16	32	≤2–64	0							4	3	57	180	68	5	0	0	0	0
SXT	>64	>64	4–128	100		0	0	0	0	0	0	4	6	8	5	8	286
Ciprofloxacin-resistant (20)
Ampicillin	512	512	4–512	90					0	0	0	2	0	0	0	0	0	2	16	0
Ciprofloxacin	16	>16	4–32	100	0	0	0	0	0	0	0	1	3	7	9
Mecillinam	2	16	≤0.5–16	10					3	4	3	3	5	2	0	0	0	0	0	0
Nitrofurantoin	16	32	2–32	0							4	0	0	7	9	0	0	0	0	0
SXT	>64	>64	8–128	100		0	0	0	0	0	0	0	1	0	0	0	19

^aResistance breakpoints used were those defined by NCCLS M100-S9 (8). They were as follows: for ampicillin ≥32 μg/ml; for ciprofloxacin, ≥4 μg/ml; for nitrofurantoin, ≥128 μg/ml; and for SXT, ≥4/76 μg/ml. The mecillinam resistance breakpoint used was ≥16 μg/ml.