Required Practical

• Use aseptic techniques
• 1. Pour hot agar into the sterile Petri dish and leave to cool and set.
  2. use a sterile dropping pipette and a spreader to evenly spread the bacteria
  3. Soak paper discs in different types or concentrations of antibiotics and antiseptics for the same length of time and place them evenly on the agar plate with the bacterial covering.
  4. Place a disc that has been soaked in sterile water onto the plate as a control
  5. Tape the lid onto the Petri dish and leave to incubate upside down for 48 hours
• Result - there should be clear areas surrounding the discs of paper which is where the bacteria have been killed. They are called inhibition zones
• Result - the more effective the treatment is at killing bacteria, the larger the inhibition zone
• Increasing the concentration of the solution increases the size of the inhibition zone
• Some bacteria may be antibiotic-resistant and will be able to grow in the presence of treatment so there will be no inhibition zone
• No inhibition zone around the water - therefore it is the antibiotic/antiseptic that kills the bacteria
• Measuring inhibition zones

  To compare how effective different treatments are, you should work out the area of inhibition zones

  1. Measure the diameter of the zone using a ruler
  2. Half the diameter to get the radius
  3. Use pi x r squared to find the area