Table 1.

Interpretative criteria for E. coli O157:H7 using disk diffusion susceptibility testing reported as inhibition zone diameters (mm)

Antimicrobial	Disk (μg)	Susceptible	Intermediate	Resistant	Antimicrobial class	WHO classification
Amoxicillin	25	≥17	14–16	≤13	β-lactams	Critically important
Cefoxitin	5	≥18	15–17	≤14	Cephalosporins	Critically important
Chloramphenicol	30	≥18	13–17	≤12	Phenicols	Highly important
Ciprofloxacin	5	≥31	21–30	≤20	Quinolones	Critically important
Kanamycin	30	≥18	14–18	≤13	Aminoglycosides	Critically important
Nalidixic acid	30	≥19	14–18	≤13	Quinolones	Critically important
Nitrofurantoin	300	≥17	15–16	≤14	Nitrofurans	Important
Streptomycin	10	≥15	12–14	≤11	Aminoglycosides	Critically important
Trimethoprim-sulfamethoxazole	1.25/23.75	≥16	11–15	≤10	Folate pathway inhibitors	Highly important
Tetracycline	30	≥15	12–14	≤11	Tetracyclines	Highly important