1.5.2: Performing the Streak Plate

Follow the steps listed below to complete your streak plate.

1. Begin by disinfecting your work area
2. Obtain all the necessary items to complete the exercise:

   Bunsen burner Inoculating loop Sharpie

   Bacterial stock culture (the identity of the bacteria present in the stock culture will be provided by the instructor during the laboratory session)

   Petri plate containing nutrient agar

3. Label the petri dish with the following information using the sharpie. Be sure to place the information on the bottom of the petri plate (that portion containing the agar)
   

   Figure 1. Proper labeling of a Petri plate. Credit: Sherry Smith

   Your initials Your lab section Date

   MC

4. Light your Bunsen burner. Be sure to adjust the Bunsen burner so that an inner blue cone is clearly visible. Remember, this is the hottest portion of the flame; you will sterilize your inoculating tools in this area.
5. Grasp your inoculating loop in your dominant hand holding it like a pencil. You will use the first three fingers of your dominant hand to manipulate your inoculating tool.
6. Flame the inoculating loop ensuring that it turns red hot, and then let it cool for approximately 15- 30 seconds. Do not allow the instrument to bump against anything and do not lay it down to cool.
7. Use your non-dominant hand to pick up the bacterial Stock Culture. Flick the test tube to practice suspending the bacteria in the culture. Generally, bacteria will settle in the tube and will need to be suspended for transfer.
8. Use the last two fingers of your dominant hand to remove the cap of the test tube.
9. Pass the mouth of the test tube through the flame of the Bunsen burner.
10. Use the sterilized loop to obtain a loopful of sample, without touching the sides of the test tube.
11. Hold the loop steady and pass the mouth of the tube through the flame and then recap the test tube. Place the test tube back in the test tube rack.
12. Lift one side of the Petri plate lid. (Do not completely remove the lid. Microbes present in the air will fall into the Petri plate and contaminate the sample. Always open the lid as seen in the image.) Introduce the inoculum to the surface of the media in the first quadrant by moving the loop across the surface area in as many tight streaks as
    

    Figure 2. Proper technique for partially opening a Petri plate during inoculation. Credit: Sherry Smith

13. Replace the lid and rotate the plate to position the second quadrant in place for the next step. Flame the loop and let it cool.
14. Streak the second quadrant by lifting one side of the Petri plate lid and streaking a few times across the first quadrant with your sterile loop into the second quadrant. Streak the second quadrant several more times.
15. Replace the lid and rotate the plate to position the third quadrant in place for the next step. Flame the loop and let it cool.
16. Streak the third quadrant by lifting one side of the Petri plate lid and streaking a few times across the second quadrant with your sterile loop. Streak the third quadrant several more times.
17. Replace the lid and rotate the plate to position the fourth quadrant in place for the next step. Flame the loop and let it cool.
18. Streak the fourth quadrant by lifting one side of the Petri plate lid and streaking a few times across the third quadrant with your sterile loop. Streak the fourth quadrant several more times.
19. Replace the lid. Flame the loop until it is red hot to kill remaining bacteria.
20. Incubate the Petri plate in an inverted position in the incubator at 37°C for 24-48 hours. You will examine your plates in the next laboratory session.

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