The effectiveness of antibiotics can be measured using a disc diffusion technique.
- A bacterial lawn is grown on an agar plate (either by spreading the bacteria over the plate, or by using a pour plate).
- A disc of blotting paper is soaked in antibiotic of known concentration and placed in the centre of the
- A clear circle of dead bacteria will form around the disc
- The diameter / radius of the circle of dead bacteria is proportional to the effectiveness of the antibiotic
- This can be compared to other antibiotics, as long as the same concentration of antibiotic is used. In addition, one can also compare the effectiveness of an antibiotic with a disinfectant or sanitiser (e.g. Phenol coefficient)