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Name ___________________________ Lab Section ____________
Streak Plate Method Results & Interpretation – 5 pts - You will hand this section in on the designated date.
1. A microbiologist used the three-phase streak plate
method to obtain isoloated colonies from a mixed
culture of bacteria. Based on the image to the right,
were they successful? Explain your answer. (1.5 pts)
2. If a person uses streak plate technique to obtain isolated colonies, but doesn’t succeed what are
some things he/she could have done wrong? (You must list at least two to get full credit) (2 pts)
3. Describe how the bacteria are diluted and spread out to form individual colonies using the streak plate
technique. (1.5 pts)
Alexa Campanella
Summer23
Yes the person was siccessful. They were
succesful because two different colonies are
visible; one type of bacteria that presents itself in
red colonies, and a different type that presents
itself in yellow colonies.
1) The person didn't invert the lid to keep condensation off the agar. If this happens,
bacteria colonies will move and no observable colonies will be present.
2) The person repeated the first step of the process and kept collecting a new sample of
the culture to streak across the agar which prevented the bacteria colonies from spreading
out.
The bacteria are spread out using an innoluating loop. First, you obtain a sample of mixed
bacteria colonies on an innoculating loop and streak roughly a quarter of an agar plate with
the loop. You then sterilize the loop and streak the agar again. This time, don't collect
more bacteria but streak through the originally streaked area and a small portion of unused
agar. Repeat this second part once more then let the agar incubate. By using this
technique, the bacteria are spread out or diluted across the agar which allows them to
create more colonies across the agar.
