Zone of Inhibition Calculator
Kirby‑Bauer disk diffusion susceptibility test
CLSI Standards
Zone Measurement
Petri Dish Visualization
AB
Example Measurements
CLSI Zone Diameter Breakpoints (mm)
| Antibiotic | S (≥) | I | R (≤) |
|---|---|---|---|
| Ampicillin | 17 | 14‑16 | 13 |
| Cefotaxime | 26 | 23‑25 | 22 |
| Ciprofloxacin | 21 | 16‑20 | 15 |
| Gentamicin | 15 | 13‑14 | 12 |
| Tetracycline | 19 | 15‑18 | 14 |
Source: CLSI M100, 2023
Interpretation
Susceptible: Effective therapy
Intermediate: Possible with higher dose
Resistant: Not effective