TABLE 2.

Ampicillin MICs recorded with eight media and three methods for 143 β-lactamase-negative H. influenzae isolates

Methoda	No. of isolates for which the MIC (μg/ml) was:					%b
	≤0.5	1.0	2.0	4.0	≥8.0	S	I	R
Microdilution (broth)
HTMc	70	15	13	13	32	59	9	31
LHB	67	14	14	14	34	57	10	33
Agar dilution (agar)
HTMc	65	17	15	18	28	57	10	32
LHB	60	17	15	14	37	54	10	36
WHB	65	12	7	15	44	54	5	41
Chocolate	62	10	8	14	49	50	6	44
Fildes	67	12	14	7	43	55	10	35
Iso-Sensitest	68	15	8	13	39	58	6	36
E-test (agar)
HTM	82	15	29	17	0	68	20	12
LHB	69	22	11	40	1	64	8	29
WHB	74	21	13	33	2	66	9	24
Chocolate	71	22	11	37	2	65	8	27
Fildes	70	23	8	36	6	65	6	29
Iso-Sensitest	74	16	15	29	9	63	10	27

^aSee Table 1 for definitions of media. 

^bPercent susceptible (MIC, ≤1.0 μg/ml) (S), intermediate (MIC, 2.0 μg/ml) (I), or resistant (MIC, ≥4.0 μg/ml) (R). 

^cRepresents tests that conform to NCCLS procedures (14).