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Biology LibreTexts

13.3: Testing environments for the Presence of Bacteria/Fungi

  • Page ID
    24208
  • Testing for Bacteria/Fungi

    Materials

    • agar plates
    • sterile swabs
    • wax pencil or marker
    • moist kitchen sponge
    • sterile water
    • hand soap

    Bacteria and also fungi (includes molds) inhabit many different environments. In the following procedure, you will test unwashed and washed hands, a kitchen sponge, and a fomite (inanimate object that may harbor bacteria) for the presence of bacteria and fungi. Fungi can be distinguished from bacteria by a fuzzy appearance.

    Hypothesis

    Hypothesize about which environment(s) will exhibit the greatest number of bacteria and which might contain fungi. What is the basis for your hypothesis?

    Procedure

    1. Obtain 2 agar plates. Hold the lid on and draw a line with a wax pencil on the bottom of the plates to divide the plates into two equal halves. The bottom of the plate contains the agar.
    2. In small letters label the areas “unwashed”, “washed”, “sponge”, “fomite”. Write your initials on the plates. Label the bottom of the dish, not the lid.
    3. Select one person to be the test subject. Lightly press three fingers on the agar on the side of plate marked “unwashed”. Do not break the agar. Close the dish. Wash hands with soap, dry, and repeat procedure on the side of the plate marked “washed”.
    4. Obtain a small piece of the moist sponge. Open the plate and lightly press the sponge onto the agar. Return the sponge. Close the dish.
    5. Dip a sterile cotton swab into the sterile water. Select a fomite to swab: cell phone, door knob, drinking fountain, etc. Lightly streak the swab on the region of the plate marked “fomite”.
    6. Tape the two plates together. Place plates at room temperature and observe during the next laboratory.