2.2: Streak Plate Technique Procedure
Quadrant Streak Plate Procedure
Name: _____________________________________________________
Course Section: ______________________________________________
The following activity will teach students how to complete a Quadrant Streak with the goal of generating isolated, pure colonies for colony morphology. Read the following procedure carefully before starting the activity
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Materials |
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Procedure |
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Students will select 1 bacterial species and work alone for this experiment. After incubation, students will compare results with classmates to compete the results chart.
Step 1: Label the bottom of the nutrient agar plate with student initials, course section, date, and the bacteria selected.
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Step 2: Heat an inoculation loop in the incinerator for at least 10 seconds until the wire is red/orange.
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Procedure |
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Step 3: Once the loop is cool, aseptically collect 1 colony from the stock plate. You do not need to swipe or gather a large amount of bacteria.
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Step 4: Sterilize the loop again and allow it to cool. Then, place the loop on a small portion of the quadrant 1 streak.
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Step 5: Sterilize the loop again and repeat Step 4, this time dragging bacteria from quadrant 2 into quadrant 3.
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Results
In table below, record the 4 colony morphology characteristic listed for your streak plate. Then, compare results with 3 other classmates to fill in the morphologies for the remaining bacterial species.
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| Bacterial Species | General Shape and Color | Colony Margin | Colony Elevation | Colony Size |
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Escherichia coli
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Serratia marcescens
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Micrococcus luteus
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Staphylococcus epidermidis
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General Questions
1. Which bacterial species did you use for your streak plate? Did you successfully obtain isolated colonies?
2. What are potential errors that may result in a failed streak plate?
3. Explain the importance of the streak plate technique in microbiology.
4. Based on proper streak plate technique, which area of the plate will always have:
- The most microbial growth:
- The least microbial growth:
5. Why can isolated, single colonies be used to generate pure cultures?
Health-Related Questions
1. How are microbiology streak plate and culture techniques useful for diagnosing strep throat?
2. A patient went to the doctor's office for a sore throat and fever. The doctor took a throat swab of the patient for a culture test, but no bacteria grew. Is Streptococcus pyogenes the causative agent of this infection? Why or why not?
Attributions
"Microbiology Laboratory Manual: Labs, 1.8 Plating on Petri Plates for Isolation" by Dr. Rosanna Hartline , LibreTexts: Biology , West Hills College Lemoore is licensed under CC BY-NC-SA 4.0
Image Citations
Procedure Image, The 4 streak plate images used in the procedure table were modified from:
- Streak plates 1.svg by Reytan, Wikimedia Commons is in the Public Domain
- Streak plates 2.svg by Reytan, Wikimedia Commons is in the Public Domain
- Streak plates 3.svg by Reytan, Wikimedia Commons is in the Public Domain
- Streak plates 4.svg by Reytan, Wikimedia Commons is in the Public Domain