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Streak Plate

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Student: Yi-Ren Wang
Course: BIO-205 BD2 Microbiology
Instructor: Dirk VandePol
Date: 6/21/2013

Streak Plate Isolation for Obtaining Pure Culture

1. When an agar plate is inoculated, why is the loop sterilized after the initial inoculation in put on? Ans: We use agar plate to inoculate microbes by zipping the loop on the agar several times. We streak on the agar plate four time, propose is to isolate the unknown bacteria. Therefore, the first time to streak on the plate, there are million of bacteria on the loop. For that reason, we need to sterilize the loop before next streaking. Then we can get small group of colonies out from the large group of colonies to observe and distinguish the unknown bacteria.

2. Define pure culture, a mixed culture?
Ans: Pure culture is mean that only contain single species bacteria in the culture. If we plate out it onto the surface of a solid medium, colonies will shown in the same size, color, and shape. On the other side, a mixed culture is a culture including more than one species bacteria.

3. Define a bacterial colony. List four characteristics by which bacterial colonies may be distinguished? Ans: A group of bacteria derived from only one species of bacteria in a specific area. There are many characteristics could be distinguished different colonies, such as, shape, size, color, and consistency.

4. Why should a Petri dish not be left open for any extended period of time? Ans: A Petri dish is a medium which using to grow bacteria cultures. If we leave the plate open on the air, it might increase the probability that microbes culture we don’t expect growing in the Petri dish.

5. Why does the streaking method you used to inoculate your plates result in isolated colonies? Ans: we streak four times on the plate in order to isolate the growing colonies. Each step of streaks we need to sterilize the loop in the flame, which is beginning and ending of the streak. We can surely relate on...