Antibiotic Sensitive (mm) Intermediary (mm) Resistant (mm)
Ampicillin ≥ 17 14-16 ≤  13
Colistin sulphate ≥ 11 9-10 ≤  8
Florfenicol ≥ 18 15-17 ≤  14
Nitrofurantoin ≥ 16 13-15 ≤  12
Novobiocin ≥ 17 15-16 ≤  14
Tetracycline ≥ 19 15-18 ≤  15
(Source: Clinical and Laboratory Standard Institute, 2006)
Table 1: Breakpoints for 6 antibiotics according to the Clinical and Laboratory Standard Institute Standards.