Culturing microorganisms

• How could you measure the zone of inhibition?

  Use a ruler to measure from a point on one side to a point directly opposite, with the lid still in place, measure again at 90* to the first diameter measurement in order to calculate a mean
• Describe how you could investigate the effect of antibiotics on bacterial growth using zones of inhibition

  Divide an agar plate with bacteria into three segments, use forceps to place filter paper discs with antiseptic in each zone, loosely tape lid onto the agar plate to allow oxygen to reach the bacteria, incubate at 25* for 48 hours, measure the diameter of clear zones using a ruler from two opposite directions - calculate the mean of measurements, calculate the area of clean zones
• Name 6 antiseptic techniques that can be used to avoid infection

  Spray the working area with disinfectant and wipe it dry, wash hands with antibacterial wash, flame the neck of the culture bottle, lift the agar plate lid at an angle, dip spreader in ethanol and pass through the bunsen flame before spreading bacteria, use forceps to place antibiotic discs
• Why should you not completely seal the agar plate?

  To allow oxygen to enter the agar plate, preventing the growth of harmful anaerobic bacteria
• Why is it necessary to measure the diameter of the zone of inhibition twice?

  Clear zones are not always uniform - taking more than one measurement allows a mean diameter to be calculated
• What equation is used to calculate the area of clear zones?

  Area = TTr^2