| Diameter of the inhibition zone (Δ) | sensitivity of the germ | Symbol |
| Δ < 7 mm | Resistant | − |
| 7 mm ≤ Δ < 8 mm | Sensitive | + |
| 8 mm ≤ Δ < 9 mm | Moderately sensitive | ++ |
| Δ ≥ 9 mm | Very sensitive | +++ |