Design and conduct a practical investigation relating to the microbial testing

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Describe a variety of infectious diseases caused by pathogens, including microorganisms, macroorganisms and non-cellular pathogens, and collect primary and secondary-sourced data and information relating to disease transmission, including: (ACSBL097, ACSBL098, ACSBL116, ACSBL117)

  • design and conduct a practical investigation relating to the microbial testing of water or food samples

Practical investigation relating to the microbial testing of water or food samples

  • Materials
    • food samples (bread, yoghurt, cheese)
    • Agar plates
    • Inoculating loops
    • Bunsen burner
    • Alcohol
    • Test tubes
    • Marking pen
    • Sticky tape
  • Method
    1. Wipe all surfaces down with alcohol.
    2. Sterilise your test tubes.
    3. In separate test tubes mash small amounts of each food with 2mL distilled water.
    4. Sterilise your inoculating loop by passing it through a flame.
    5. Dip the inoculating loop into your food type and wipe it gently over the surface of an agar plate.
    6. Sterilise the loop again and repeat the procedure twice so that three agar plates are prepared for each treatment.
    7. Set aside 3 agar plates to act as controls.
    8. Close and seal each agar plate with sticky tape, then label it with a marking pen.
    9. Examine the plates after 15 days and count the number of fungi colonies and the number of bacterial colonies.
  • Safety
    1. Be careful when using the Bunsen burner and hot inoculating loop.
    2. Only open the agar plate a little bit, to avoid mouth bacteria entering the plate.
    3. Wear gloves to avoid transmission of bacteria.
    4. Once the agar plate is sealed off, do not open it again.
    5. Wash hands thoroughly before leaving the laboratory.

Extract from HSC Biology Stage 6 Syllabus. © 2017 Board of Studies NSW.