RP-agar plates

• how do you prepare for an uncontaminated culture?

  1. Pour hot agar into the sterile petri dish and leave to cool and set. use a sterile dropping pipette and spreader to evenly spread the bacteria 
  2. Soak paper discs in different types or concentrations of antibiotics and antiseptics for the same length of time and place them on the agar plate with the bacterial covering. This allows the antibiotic or antiseptic to diffuse into the agar. 
  3. Place a disc that has been soaked in sterile water onto the plate as a control.
  4. Tape the lid onto the petri dish and incubate upside down for 48 hrs
• how to analyse results from uncontaminated culture practical

  • should be clear areas surrounding some discs of paper which is where the bacteria have been killed inhibition zones.
  • The more effective the treatment is at killing the larger the zone.
  • Increasing the concentration of the solution increases the size of inhibition
  • Some bacteria is antibiotic-resistant and will be able to grow in the presence of the treatment so no inhibition zone. 
  • You should notice that there is no inhibition zone around the control disc and therefore it is the antibiotic/antiseptic that kills the bacteria.