required practical: microbiology

• What antiseptic techniques can be used to avoid contamination?

  1. Spray working area with disinfectant and wipe dry

  2. Wash hands with antibacterial wash

  3. Flame the neck of the culture bottle

  4. Lift the lid of the agar plate at an angle

  5. Dip spreader in ethanol and pass through Bunsen flame before spreading bacteria

  6. Use forceps to place antibiotic discs
• Describe how you could 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 (zones of inhibition) using a ruler from two opposite directions - calculate mean of measurements

  6. Calculate area of clear zones
• How would you measure the zone of inhibition?

  • Use a ruler to measure from a point on one side to a point directly opposite (with lid still in place)
  • Measure again at 90° to first diameter measurement in order to calculate a mean
• Why should you not completely seal the Agar plate?
• Why is it necessary to measure the diameter of the zone of inhibition twice?
• What equation is used to calculate the area of clear zones?

  Area = πr2