TABLE 3.

Ampicillin disk susceptibility tests on six different agar media for 143 β-lactamase-negative strains of H. influenzae

Agar mediuma	No. of strains with the following zone diam (mm):									%b
	≥24	23	22	21	20	19	18	17	≤16	S	I	R
HTMc	82	8	8	8	16	14	4	3	0	68	27	5
LHB	79	9	1	5	8	12	6	11	12	62	17	20
WHB	82	4	5	5	5	12	14	9	7	64	15	21
Chocolate	80	7	2	7	7	9	14	9	8	62	16	22
Fildes	92	1	2	2	10	4	13	10	9	68	10	22
Iso-Sensitest	90	1	4	4	6	6	6	12	14	66	11	23

^aSee Table 1 for definitions. 

^bPercent susceptible (≥22 mm) (S), intermediate (19 to 21 mm) (I), or resistant (≤18 mm) (R). 

^cRepresents tests that conform to the NCCLS disk test procedure (13).