Microbiology

• What antiseptic techniques can be used to avoid contamination? ● Spray working area with disinfectant and wipe dry ● Wash hands with antibacterial wash ● Flame the neck of the culture bottle ● Lift the lid of the agar plate at an angle ● Dip spreader in ethanol and pass through Bunsen flame before spreading bacteria ● Use forceps to place antibiotic discs
• Describe how you could investigate the effect of antibiotics on bacterial growth using zones of inhibition ● Divide agar plate with bacteria into three segments ● Use forceps to place filter paper disc with antiseptic in each zone ● Loosely tape lid onto agar plate to allow oxygen to reach bacteria ● Incubate at 25°C for 48 hours ● Measure the diameter of clear zones (zones of inhibition) using a ruler from two opposite directions - calculate mean of measurements ● Calculate area of clear zones
• What equation is used to calculate the area of clear zones? Area = πr2
• 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 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
• Why should you not completely seal the Agar plate? To allow oxygen to enter the agar plate, preventing the growth of harmful anaerobic bacteria