Bacterial Streak Plate
An agar streak plate is a common microbiological technique used to isolate and obtain pure colonies of microorganisms from a mixed culture. Here's a basic protocol for performing an agar streak plate:
Materials Needed:
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Microbial culture (mixed culture or sample)
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Nutrient agar plates (or specific medium depending on your microorganism)
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Inoculating loop or bacteriological loop
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Bunsen burner or alcohol burner
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Personal protective equipment (lab coat, gloves, safety goggles)
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Labels and marker
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Incubator (if necessary)
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Petri dish disposal method
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Procedure:
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Preparation:
a. Ensure that your work area is clean and organized. Put on appropriate personal protective equipment (PPE) such as a lab coat, gloves, and safety goggles.
b. Label the bottom of an agar plate with relevant information such as date, sample source, and any other identifiers.
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Inoculation:
a. Using a sterilized inoculating loop, obtain a small amount of the mixed culture or sample you want to isolate.
b. Lift the lid of the agar plate slightly and streak the inoculum onto the surface of the agar by making a series of streaks across the plate, moving from the outer edge to the center.
c. Close the lid of the plate.
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Sterilization of Loop:
a. Flame-sterilize the inoculating loop by holding it in the flame of a Bunsen burner or alcohol burner until it turns red-hot.
b. Allow the loop to cool briefly by touching it to the agar away from the inoculated area.
Second Streak:
a. Lift the lid slightly and streak the loop back and forth through the first streak, starting from the end closest to the inoculum and moving towards the untouched area of the agar.
b. Avoid going over the same path as the first streak. This will dilute the sample and promote isolation of individual colonies.
c. Close the lid of the plate.
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Sterilization of Loop and Third Streak:
a. Sterilize the loop again by flame-sterilizing it and allowing it to cool.
b. Streak the loop back and forth through the second streak, aiming to isolate individual colonies even further.
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Final Streak (Optional):
a. If needed, you can repeat the sterilization of the loop and streak a fourth time for additional isolation.
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Incubation:
a. Place the inoculated agar plate upside-down in an incubator set to the appropriate temperature and conditions for the growth of your microorganism. Follow the recommended incubation period.
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Colonial Isolation and Storage:
a. After incubation, individual colonies should have grown on the agar plate.
b. Using a marker, circle or label any isolated colonies that appear on the plate.
c. If you need to store isolated colonies for further analysis, you can transfer them to fresh agar plates or store them in appropriate culture media or preservation methods.
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Disposal:
a. Properly dispose of used agar plates and inoculating loops according to your institution's biohazard waste disposal procedures.
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Remember to follow your laboratory's safety guidelines and protocols while performing agar streak plate techniques. The specific details of this protocol might vary depending on the type of microorganisms you are working with, so always consult with your lab supervisor or refer to relevant literature for specific recommendations.