RP02 - Microbiology

• What is the aim of the microbiology practical?

  To investigate how different antiseptics or antibiotics affect bacterial growth using agar plates by measuring zones of inhibition.
• What is Step 1 in the microbiology practical?

  Clean – Disinfect the bench and wash hands with antibacterial soap.
• Why is it important to clean the bench and your hands?

  To prevent contamination of the experiment with unwanted microbes.
• What is Step 2 in the microbiology practical?

  Label – Mark 3 segments on the base of the agar plate, add a central dot to each, and label with initials, date, and bacteria name.
• Why should the petri dish be labelled underneath, not on the lid?

  So you can still identify the sample after the lid is removed or rotated.
• What is Step 3 in the microbiology practical?

  Sterilise – Use aseptic technique by flaming the glass spreader and keeping the petri dish only slightly open facing the Bunsen flame.
• What does aseptic technique prevent?

  It prevents contamination by killing unwanted microbes and keeping new ones out.
• What is Step 4 in the microbiology practical?

  Prepare – Soak filter paper discs in different antiseptics. Use forceps to place one on each dot in the segments of the plate.
• Why use forceps when placing the discs?

  To avoid touching the discs and introducing other microbes.
• What is Step 5 in the microbiology practical?

  Seal – Tape the dish with 2 pieces of tape, not all the way around, to allow oxygen in.
• Why should the petri dish not be sealed all the way around?

  To prevent anaerobic (dangerous) bacteria from growing due to lack of oxygen.
• What is Step 6 in the microbiology practical?

  Incubate – Place the dish in an incubator at 25°C for 48 hours.
• Why is the dish incubated at 25°C instead of body temperature (37°C)?

  To reduce the risk of culturing harmful pathogens.
• What is Step 7 in the microbiology practical?

  Measure – Measure the diameter of the clear zones (zones of inhibition) twice at 90° angles and take the mean.
• What is a zone of inhibition?

  The clear area around a disc where bacteria have not grown due to the antiseptic.
• What is Step 8 in the microbiology practical?

  Calculate – Use the formula:

  Area = πr² or πd² ÷ 4
• Why do we calculate the area of inhibition zones?

  To compare how effective each antiseptic or antibiotic is against bacteria.
• What is the extension task for this practical?

  Repeat the experiment using different concentrations of the same antiseptic to find the optimum strength.
• What safety precautions should be followed during RP02?

  Wear goggles when using Virkon, and wash hands before and after handling bacteria.
• What are two possible sources of error in this practical?

  Irregular shape of inhibition zones making measurement harder.

  Contamination from other microbes affecting results.
• What is the core setup equipment for RP02?

  Agar plate, heatproof mat, filter paper discs, incubator at 25°C.
• What is the antiseptic & chemical equipment for RP02?

  3 antiseptics (e.g. mouthwash, TCP, antiseptic cream), disinfectant bench spray, 1% Virkon, antibacterial handwash.
• What tools are needed to handle and label in RP02?

  Forceps, clear tape, wax pencil or permanent marker.