cpac 13

• Aseptic technique


  • Used to avoid contamination of the sample from outside substances, such as microorganisms
  • Important to get reliable and repeatable data
• Streak plating


  • Technique in which bacteria are spread out on a nutrient agar plate so that distinct individual colonies can be seen
  • Colonies can then be grown on clean agar plates to produce non-contaminated samples of one species of bacteria
  • Colonies can be identified as a particular species of bacteria via indicators such as the size, colour and texture of the colony
• 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
• Equipment


  • Bench disinfectant
  • Paper towels
  • Bunsen burner
  • Inoculating loop
  • Mixed culture of bacteria
  • Three nutrient agar plates
  • Adhesive tape
• Method


  1. Loosen the cap of the mixed culture tube

  2. Flame the inoculating loop to sterilise

  3. Flame the neck of the mixed culture tube to sterilise

  4. Dip the inoculating loop into the mixed culture

  5. Flame the neck of the mixed culture tube again and replace the lid

  6. Open the petri dish lid as little as possible. Make four streaks from one 'corner' of the plate to an adjacent 'corner'

  7. Turn the plate ninety degrees and make another three/four streaks at a nine degree angle from the first

  8. Flame the inoculating loop again

  9. Tape the lid of the Petri dish and leave for 24 hours in an incubator

  10. Observe and sketch the plates and take a sample of a white colony using an inoculating loop

  11. Take a sample of a yellow colony using an inoculating loop

  12. Tape the lid of the Petri dishes and leave for 24 hours in an incubator

  13. Observe and sketch the plates
• White colonies are likely to be Salmonella. Yellow colonies are likely to be Staphylococcus.
• Hazards


  • Disinfectant
  • Biohazard
  • Naked flame
• Biohazard


  Contamination; infection
• Naked flame


  Fire hazard; burns
• Safety Precautions


  1. Keep disinfectant away from naked flame

  2. Use disinfectant; wash hands with soap after dissection; do not incubate at human body temperature; do not open agar plate post incubation

  3. Keep away from flammable materials; tie up long hair; keep away from edge of desk
• In Emergency


  1. Put out fire; seek assistance

  2. Seek assistance

  3. Put out fire; seek assistance; run burns under cold water immediately
• Risk Level: Low for disinfectant, Low/medium for biohazard (depends on likeliness of bacteria sample used to cause infection), Low for naked flame