How to Streak a Bacterial Culture
From your Biology Guide

Procedure on how to isolate bacterial colonies by using the streaking method.

Difficulty Level: Easy    Time Required: 5 minutes

1. Sterilize an inoculating loop by placing it at an angle over a flame.
2. Remove the lid from a culture plate containing the desired microorganism.
3. Cool the inoculating loop by stabbing it into the agar in a spot that does not contain a bacterial colony.
4. Pick a colony and scrape off a little of the bacteria using the loop. Be sure to close the lid.
5. Using a new agar plate, lift the lid just enough to insert the loop.
6. Streak the loop containing the bacteria at the top end of the agar plate moving in a zig-zag horizontal pattern until 1/3 of the plate is covered.
7. Sterilize the loop again in the flame and cool it at the edge of the agar away from the bacteria in the plate that you just streaked.
8. Rotate the plate about 60 degrees and spread the bacteria from the first streak into a second area using the same motion in step 6.
9. Sterilize the loop again using the procedure in step 7.
10. Rotate the plate about 60 degrees and spread the bacteria from the second streak into a new area in the same pattern.
11. Sterilize the loop again.
12. Replace the lid and invert the plate. Incubate the plate over night at 37 degrees Celsius.
13. You should see bacterial cells growing in streaks and in isolated areas.
    

Tips:

1. When sterilizing the inoculating loop, make sure that the entire loop turns orange before using on the agar plates.
2. When streaking the agar with the loop, be sure to keep the loop horizontal and only streak the surface of the agar.

Related Information:

• Bacteriology
  

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