Lab 5 - Quadrant Streak

Question 1

what does the streak plate technique allow us to do?

Answer 1

it is a very important technique in microbiology and allows us to create isolated colonies of bacteria

Question 2

what is an isolated colony?

Answer 2

isolated colony = pure culture of one type of bacterium

Question 3

when one bacterium falls off the loop onto the plate, it divides into more than 1 million bacteria, forming what?

Answer 3

forming a visible colony

Question 4

what does the quadrant streak help us do?

Answer 4

now we can now work with a known pure culture of bacteria

Question 5

what is the goal of the quadrant streak?

Answer 5

to progressively dilute bacteria, not add bacteria

Question 6

what is colony morphology?

Answer 6

the size, shape, color, texture, and optical properties of a colony. it depends on the kind of microbe, type of media, and length/temperature of incubation

Question 7

what are the steps of quadrant streaking?

Answer 7

1. Sterilize loop and get a loopful of culture
2. Mentally divide plate into 4 areas
3. Streak loop back and forth several times across area 1
4. Sterlize loop again and cool
5. Start in area 1 and pull bacteria into area 2 and finish streaking it.
6. Sterilize loop again and cool.
7. Start in area 2 and streak to area 3.
8. Sterilize loop again and cool.
9. Start in area 3 and streak into area 4.
10. Sterilize loop.

Question 8

Imagine a new bacterial species is discovered by one group of scientists. They report that it produces round, entire, flat colonies that are 2 mm in diameter after incubating for 12 hours. Another group of scientists starts working with the exact same bacterial species. They find it what produces irregular, curled, convex colonies that are 3 mm in diameter incubating for 12 hours.
Assuming that these two groups of scientists are indeed working with the same microorganism, propose a reason why the colony morphologies they observe are vastly different.

Answer 8

Due to different environments, what the growth medium is, the temperature of incubation.

Question 9

Bacteria X and Y are found in your patient. You are trying to figure out what they are. You know Bacteria X can ferment (partially break down) sorbitol, a type of carbohydrate. Bacteria X cannot ferment the lactose (a type of sugar). The situation is reversed for Bacteria Y. You need to see if Bacteria X is present in the culture. By performing a sorbitol and lactose fermentation test, what would the results be?

Answer 9

The patient’s mucus (our example) has Bacteria X. Bacteria X can eat sorbitol, and ferment it. This creates turbidity.
The mucus also has bacteria Y. Bacteria Y can ferment lactose. This also creates turbidity.
So, what we have to do is now perform the quadrant streak to isolate both bacteria into separate colonies. This way you can test the 2 colonies for sorbitol and lactose. That way it is more clear.