RP15

• Investigate the effect of different antibiotics on bacteria

  1. Carry out the whole experiment using aseptic technique

  2. Flame the forceps and pick up a paper disc

  3. Slightly lift the lid of the petri dish and place the paper disc onto the agar

  4. Tape the dish with two pieces of sellotape

  5. Wash your hands and disinfect the bench

  6. Incubate for 24 hours at approximately 30 degrees
• Aseptic technique


  Used to avoid contamination of the sample from outside substances, such as microorganisms
• Aseptic technique


  • Important to get reliable and repeatable data
• Zone of inhibition


  Can be used to measure the effectiveness of different antibiotics against particular species of bacteria
• Equipment


  • Agar plate seeded with bacteria
  • Pipette
  • Bunsen burner
  • Disinfectant
  • Soap
  • Paper towels
  • Forceps
  • Antibiotic impregnated paper discs
  • Sellotape
  • Incubator
• Aseptic Technique


  1. Wipe down surfaces with antibacterial cleaner both before and after experiment

  2. Use a Bunsen burner in the work space so that convection currents draw microbes away from the culture

  3. Flame the wire hoop before using to transfer bacteria

  4. Flame the neck of any bottles before use to prevent any bacteria entering the vessel

  5. Keep all vessels containing bacteria open for the minimum amount of time

  6. Close windows and doors to limit air currents
• Aseptic technique is used to avoid contamination of the sample from outside substances, such as microorganisms
• Aseptic technique is important to get reliable and repeatable data
• Inoculating an antibiotic agar plate, growing bacteria on it and then determining zone of inhibition can be used to measure the effectiveness of different antibiotics against particular species of bacteria
• The area of the zone of inhibition/ 'clear zone' will be more effective when the antibiotics are more effective against the type of bacteria being used
• How effective an antibiotic is against a certain type of bacteria is dependent on whether the bacteria are gram-positive or gram-negative and what type of antibiotics are used