Table 1.

The Guidelines Used to Determine the Antimicrobial Resistance Breakpoints Using the Disk-Diffusion and Broth Microdilution Methods

	Result for method
	Broth microdilution				Disk diffusion
		MIC breakpoints (μg/ml)				Zone diameter breakpoint (mm)
Antimicrobial agent	Test range (μg/ml)	S	I	R	Disk conc. (μg)	S	I	R
Ampicillin	0.03–64.0	≤8	16	≥32	10	≥17	14–16	≤13
Ciprofloxacin	0.03–64.0	≤1	2	≥4	5	≥21	16–20	≤15
Erythromycin	0.03–64.0	≤8	16	≥32	15	≥23	14–22	≤13
Gentamicin	0.03–64.0	≤2	4	≥8	10	≥15	13–14	≤12
Streptomycin	0.03–64.0	≤2	4	≥8	10	≥15	12–14	≤11
Tetracycline	0.03–64.0	≤4	8	≥16	30	≥15	12–14	≤11
Tylosin	0.03–64.0	≤4	8	≥16	NT	—	—	—
Azithromycin	NT	—	—	—	15	≥18	14–17	≤13
Chloramphenicol	NT	—	—	—	30	≥18	13–17	≤12
Nalidixic acid	NT	—	—	—	30	≥19	14–18	≤13

I, intermediate; MIC, minimum inhibitory concentrations; NT, not tested; R, resistance; S, susceptible.