4.12—Core Practical 9 - antimicrobial properties of plants

To investigate plant antimicrobial properties, spread a known bacterial culture over nutrient agar, place equal paper discs containing plant extracts and a solvent control, then incubate safely and measure the clear zones.

Prepare extracts consistently, use sterile equipment, open plates briefly, tape and invert them, and incubate at a safe temperature. Measure diameters or areas, repeat at least three times and calculate a mean.

If a disc gives a 12 mm diameter zone, calculate its area using the radius, not the diameter. Compare that mean with the ethanol control before claiming an extract inhibits growth.

Aseptic technique protects the culture and the people handling it; it is not an optional decoration. A larger zone can also reflect faster diffusion, so concentration and disc size must be controlled.