Table 1.

Reproducibility results of the colorimetric-plate method in antimicrobial susceptibility testing of Escherichia coli

Antimicrobiala	No. of isolatesb	No. of testsc	No. of test results in interpretive categorye:			Reproducibility result, % (no.)d
			S	I	R	CA	VMD	MD	mD
Ampicillin	10	270	108	0	162	100	0	0	0
Ampicillin-sulbactam	10	270	169	47	54	97.4	0	0	2.6 (7)
Cefazolin	10	270	162	0	108	100	0	0	0
Cefuroxime	10	270	162	0	108	100	0	0	0
Ceftriaxone	10	270	163	27	80	99.6	∼1.3 (1)	0	0
Cefepime	10	270	270	0	0	100	0	0	0
Imipenem	10	270	270	0	0	100	0	0	0
Amikacin	10	270	216	2	52	99.3	0	0	0.7 (2)
Gentamicin	10	270	192	50	28	98.5	0	0	1.5 (4)
Ciprofloxacin	10	270	189	0	81	100	0	0	0
Co-trimoxazole	10	270	162	0	108	100	0	0	0
Nitrofurantoin	10	189	189	0	0	100	0	0	0
All antimicrobials	10	3,159	2,252	126	781	∼99.5	0.1 (1)	0	0.4 (13)

^aNitrofurantoin was not tested in isolates of nonurine origin.

^bE. coli ATCC 25922 (of nonurine origin) and nine clinical E. coli isolates, of which two were of nonurine origin.

^cIsolates tested in three replicate tests at three distinct sites in three different days.

^dReproducibility was acceptable if the results showed ≥95% category agreement compared to the test mode (i.e., the most frequent test result for the isolate) as a reference. CA, categorical agreement; VMD, very major discrepancy; MD, major discrepancy; mD, minor discrepancy.

^eS, susceptible; I, intermediate; R, resistant.