Table of Contents
How does streaking allow you to get single colonies?
As the original sample is diluted by streaking it over successive quadrants, the number of organisms decreases. Usually by the third or fourth quadrant only a few organisms are transferred on the inoculating loop and these produce a few isolated colonies.
Why does the quadrant streaking method result in isolated colonies?
Why does the streaking methods you used to inoculate your plates result in isolated colonies? This begins to dilute the bacteria by spreading it over distance and eventually the bacteria are spaced far enough apart to form single colonies.
What is the purpose of streaking out for single colonies?
As you might guess, the purpose of streaking for isolation is to produce isolated colonies of an organism on an agar plate. This is useful when you need to separate organisms in a mixed culture or when you need to study the colony morphology of an organism.
How does streaking for isolation result in single discrete colonies?
As the original sample is diluted by streaking it over successive quadrants, the number of organisms decreases. Usually, by the third or fourth quadrant, only a few organisms are transferred which will give discrete colony forming units (CFUs).
Why must loops be cooled first?
The inoculating loop must be cooled before it touches the surface of the medium. The loop must be cooled to prevent killing the bacteria. If the loop is too hot, it will kill the bacteria and sizzle and melt the media that further promotes contamination.
Why do you sterilize the wire loop between streaking each quarter of the plate?
Flame the loop or use a new disposable loop after you streak each quadrant. Using a new or sterilized loop allows you to effectively dilute the inoculum on the plate and obtain isolated colonies by spreading the inoculum thinner and more evenly.
Which is better for isolation, selective broth or streak plate?
Starting your isolation with the selective broth in the second method seems to work better for enriching your higher mercury tolerant bugs.
How is the streak plate method used in mixed culture?
The most common and least expensive means of isolating organisms in a mixed culture is to use the streak plate method. The streak plate method of isolation means to spread the microbes on plated agar media so that the individual cells or colony forming units (CFUs) can become isolated and grow into individual, pure colonies.
What’s the difference between quadrant and continuous streaking?
Quadrant method. In the quadrant method, four equally sized sections are streaked. The continuous streaking method typically involves inoculating the top half of the plate, rotating it 180 degrees, and inoculating the other half of the plate without sterilizing the loop or dragging bacteria from the previous section.
How to isolate bacterial colonies using the streak plate?
Spread it in a zig-zag manner along one quadrant of the plate from the edge inward approximately 1.5 cm. Step 3: Sterilize your loop using a Bunsen burner or a “cinerator” such as this . Allow the loop to cool (without setting it down) for several seconds. Then, drag the loop gently through your first quadrant (only once.)