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Biology LibreTexts

4.4: Materials and Procedures

  • Page ID
    40172
  • Materials

    • SDA (Sabouraud Dextrose Agar)—1 plate/pair
    • TSA (Tryptic Soy Agar)—1 plate/pair
    • Sterile cotton swab in saline—2 swabs/pair

    Procedures

    Day One

    Divide into pairs for environmental sampling:

    1. Each pair will label one SDA plate and then place it open (set lid right side up next to the plate) somewhere inside or outside the lab for 15 min.
    clipboard_ed761db3ea5b24208ff1b80349197aa88.png
    Figure \(\PageIndex{1}\): Petri dish, showing how to label and invert for incubation. (C.S. Ramey)
    1. After the exposure, replace the lid and parafilm the petri dish. Place the petri dish, inverted, in the designated receptacle.
    clipboard_eda6c14dab292a0ac66d4221a964aad56.png
    Figure \(\PageIndex{2}\)
    1. Label, then divide your TSA plate in two. Take the sterile cotton swab in saline and swab a surface, then swab a line down one side of the plate. Label that side of the plate with the surface swabbed. The other partner does the same on the other side of the plate, from a different surface.
    2. Parafilm the TSA plate and incubate it, inverted, in the class incubator.

    Day Two (after several days of incubation)

    Safety

    Environmental samples are considered BSL-2 once they have been incubated. Wear gloves when handling the plates, make sure the plates are completely sealed, and DO NOT open the plates. Discard in the Biohazard trash container.

    Observe the SDA and TSA plates for growth. Look for fungi and bacterial colonies. Each colony originates from one cell/spore, which landed or was swabbed onto the plate. Over time, the cells multiplied to an extent that is finally visible to see.

    Results

    Draw your plates: Note the color and texture of different colonies viewing through the top of the plate and the bottom of the plate. Use a dissecting scope to see finer detail.

    clipboard_e76f533bad646c64d132cee8839bf93ab.png
    Figure \(\PageIndex{3}\)

    Class Results

    Table \(\PageIndex{1}\): SDA Air plates

    Pair Names

    Location/time

    Approx. # of colonies

    Table \(\PageIndex{2}\): TSA Surface plates

    Pair Names

    Surfaces Swabbed

    Approx. # of Colonies

    Contributors and Attributions

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