Streak Plate Isolation for Obtaining Pure Culture Essay

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.

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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.

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 this technique which can help us to spreading bacteria culture on the plate. So we can expect to see the single colony in the end of the streak. 6.

Why is necessary to isolate individual colonies from a mixed growth? Ans: Every individual colony in a mixed growth might present different bacteria. We isolate them to help us effectively to determine on their differences. 7. Why was blood agar, rather than a nutrient agar plate used for the culture from your mouth? Ans: Because in a blood agar contains more nutrient than a nutrient agar.

In our mouth it could have more different species bacteria that blood agar will be a great place for them to grow. 8. Are a large number of microorganisms found in the mouth a cause for concern? Explain. Ans: In my opinion, it might not necessary to worry about microorganisms in our mouth.

There are some of them are harmless bacteria, and keep balance in our mouth. Therefore, depending on the species we may take more concern. 9. How do microorganisms find their way into the mouth? Ans: there are a lot of ways microbe can go inside our mouth, such as eating food, drinking water, putting fingers on mouth.

All of them could covered with microorganisms to pass through to our mouth. Date Collection Nutrient Agar Blood Agar Describe Nutrient Agar: We use a mixed culture on this nutrient agar. As the simple we use, there are two different colonies. First of all, small circular size and light white color.

Secondly, large and flat ring size with cream color the size is bigger than first one. Blood Agar: On the blood agar we work with my mouth. I can see two different kinds of colonies on the plate. First, small dots with light white color.

Other one is white dots. It is a little bit bigger than another.

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