RP 2 - Microbiology (HT)

• What is one antiseptic technique to avoid contamination in a laboratory setting?

  Spray working area with disinfectant and wipe dry
• What should you do before handling bacterial cultures?

  Wash hands with antibacterial wash
• What is the purpose of flaming the neck of the culture bottle?

  To sterilize the neck and avoid contamination
• Why should the lid of the agar plate be lifted at an angle?

  To minimize contamination while allowing airflow
• What should you do to the spreader before spreading bacteria?

  Dip the spreader in ethanol and pass it through a Bunsen flame
• How should antibiotic discs be placed on the agar plate?

  Use forceps to place antibiotic discs
• What are the steps to investigate the effect of antibiotics on bacterial growth using zones of inhibition?

  1. Divide agar plate with bacteria into three segments

  2. Use forceps to place filter paper disc with antiseptic in each zone

  3. Loosely tape lid onto agar plate to allow oxygen to reach bacteria

  4. Incubate at 25°C for 48 hours

  5. Measure the diameter of clear zones using a ruler from two opposite directions

  6. Calculate mean of measurements

  7. Calculate area of clear zones
• How do you measure the zone of inhibition?

  Use a ruler to measure from one side to the opposite side
• Why is it important to measure the zone of inhibition at 90° to the first measurement?

  To calculate a mean diameter due to non-uniform clear zones
• Why should you not completely seal the agar plate?

  To allow oxygen to enter and prevent the growth of harmful anaerobic bacteria
• Why is it necessary to measure the diameter of the zone of inhibition twice?

  To allow a mean diameter to be calculated due to non-uniform clear zones
• What equation is used to calculate the area of clear zones?


  Area = πr²
• If the radius of a clear zone is $3 \text{ cm}$, what is the area?


  $Area =$$\pi (3 \text{ cm})^2 =$$9\pi \text{ cm}^2 \approx 28.27 \text{ cm}^2$