Testing the effectiveness of antibiotics, antiseptics, or plant extracts on microbial cultures can be carried out in the laboratory using agar plates and bacteria. This process requires careful aseptic techniques to ensure accurate and uncontaminated results.

Method A: Preparing Agar Plates with a Bacterial Colony

Sterilisation of Equipment:

• Glass Petri dishes and agar gel must be sterilised in an autoclave, or pre-sterilised plastic Petri dishes can be used.

• Reason: Sterilisation ensures that no unwanted bacteria are present, which could contaminate the experiment. Pouring the Agar:

• Pour the sterile agar into Petri dishes and allow it to set.

• Reason: The agar provides a nutrient-rich environment for the bacteria to grow. Adding Bacteria to the Agar:

• Use a sterile pipette to add a few drops of the bacterial solution to the agar. Afterward, place the pipette in disinfectant.

• Reason: This introduces the bacteria that will form a lawn on the agar surface. Spreading the Bacteria:

• Use a sterile spreader (either pre-sterilised or sterilised in ethanol) to spread the bacterial solution evenly across the agar surface.

• Reason: Spreading ensures a uniform "lawn" of bacteria across the plate. Sealing and Labelling:

• Replace the lid quickly and secure with tape, but do not fully seal the plate. Label and store the plates upside down.

• Reason: Partially sealing prevents contamination but allows oxygen in, preventing the growth of harmful anaerobic bacteria. Storing upside down stops condensation from contaminating the bacterial culture. Incubation:

• Incubate the plates at a maximum temperature of 25°C in schools.

• Reason: This prevents the growth of harmful pathogens. In medical settings, plates may be incubated at 37°C (body temperature) for faster bacterial growth.

Method B: Testing Antibiotics, Antiseptics, or Plant Extracts