TABLE 2.

Disk diffusion interpretive criteria for Neisseria meningitidis on the basis of the four-laboratory study

Antimicrobial agent (disk content in μg unless otherwise noted)	MIC (μg/ml)			Zone diam (mm)
	Susceptible	Intermediate	Resistant	Susceptible	Intermediate	Resistant
Ampicillin (10)	≤0.12	0.25-1	≥2	≥30	23-29	≤22
Penicillin (10 U)	≤0.06	0.12-0.25	≥0.5	≥32	27-31	≤26
Amdinocillina (10)	≤0.12		≥0.25	≥23		≤22
Cefotaxime (30)	≤0.12			≥34
Ceftriaxone (30)	≤0.12			≥34
Meropenem (10)	≤0.25			≥30
Chloramphenicol (30)	≤2	4	≥8	≥26	20-25	≤19
Rifampin (5)	≤0.5	1	≥2	≥25	20-24	≤19
Trimethoprim-sulfamethoxazole (1.25-23.75)b	≤0.12-2.3	0.25-4.75	≥0.5-9.5	≥30	26-29	≤25
Minocycline (30)	≤2			≥26
Azithromycin (15)	≤2			≥20
Ciprofloxacin (5)	≤0.03	0.06	≥0.12	≥35	33-34	≤32
Nalidixic acid (30)	≤4		≥8	≥26		≤25

^aAmdinocillin disks can be used to screen for nonsusceptibility to ampicillin (MIC > 0.25 μg/ml).

^bTrimethoprim-sulfamethoxazole is the preferred disk for detection of sulfonamide resistance.