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Procedures - Day One:
- Use the marking pencil to label the top edge of two agar plates with your names and the date. Mark one plate S. aureus and the other plate E.coli.
- Use the marking pencil to draw lines on the bottom of both agar plates dividing the plates into 4 sections. Number the sections 1, 2, 3 and 4 but try to make the numbers small. (Please see Figure 1)
- Be sure that the alcohol is far away from the Bunsen burner! Carefully light the Bunsen burner. Remove the cap on the S. aureus culture tube and carefully flame the culture tube opening. Insert
the sterile swab into the culture of S. aureus. Squeeze the extra fluid off of the swab by gently pressing the swab against the inner side of the culture tube. Remove the swab, flame the opening of
your culture tube and recap it.
- Use the swab to gently streak the entire agar surface of the plate labeled S. aureus. Be sure to turn the plate at least three times while streaking to spread the bacteria out evenly. Finally, gently
run the swab around the edge of the agar plate. Cover your plate. Discard the swab as directed by your teacher. Allow the covered plate and culture to dry for 5 to 10 minutes at room
temperature.
- Repeat steps 3 and 4 using a new sterile swab, the agar plate labeled E.coli and the E.coli culture.
- Turn the Bunsen burner off.
- Select the four antibiotics that you will be testing. In the Data table provided, record the name of the antibiotic and the section (1-4) in which you will place it. To avoid confusion place the same
antibiotic in the same section on both plates.
- Sterilize the forceps by dipping them in alcohol and allowing them to air dry. Use the sterile forceps to pick up one disk of antibiotic number 1 and place it in the center of section 1 on the S. aureus
plate. IMPORTANT: Do not touch the agar surface with forceps or place the forceps on the lab table or you will need to sterilize them again! Please do not press the antibiotic disks into the agar but be
sure that contact is made between the disks and the surface of the plate. Do not move the disk once it is placed on the agar.
- Repeat for disks 2, 3 and 4 on the S. aureus plate.
- Repeat steps 7, 8 and 9 for the E. coli culture.
- Incubate the plates at 35 degrees Celsius until the next class. Do not invert the agar plates when incubating. This will prevent the antibiotic disks from falling off overnight.
- Clean the lab area and wash your hands.
S. aureus E.coli
Fiqure 1 |
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