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.