Culturing microorganisms - RP

• How do you measure the zone of inhibition?


  Use a ruler to measure and measure again 90 degrees away 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 degrees for 48 hours, measure the diameter of clear zones using a ruler from two opposite directions, calculate the mean of measurements and 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 the 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?


  Oxygen can enter the agar plate, preventing 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 squared