Exercise 6: Pure Cultures: Preparing Streak Plates

Question 1

Define “pure culture.”

Answer 1

A group of bacteria that is of one species.

Question 2

What is the purpose of a streak plate?

Answer 2

It is used to obtain a pure culture of a bacterial organism.

Question 3

Name the three steps of the T-streak.

Answer 3

1. The top third of the agar plate (called the area of heavy inoculum) is inoculated with a substantial amount of bacteria
2. The loop is sterilized and cooled to drag some cells from the area of heavy inoculum to the left side of the agar with a zigzag pattern
3. The loop is resterilized and cooled to drag cells from the left side of the agar to the right side

Question 4

What is the purpose of step 1 of a T-streak?

Answer 4

It is supposed to serve as a pool of living cells to pull from as the streak continues.

Question 5

What is the purpose of step 2 of a T-streak?

Answer 5

It is supposed to drag a handful of cells from the pool in the area of heavy inoculum so that the number of cells in that left section is greatly reduced

Question 6

What is the purpose of step 3 of a T-streak1?

Answer 6

The final step is meant to drag a few cells to the right side of the agar so that they will develop into individual colonies.

Question 7

Name some possible problems that can occur with the T-streak.

Answer 7

Using the loop incorrectly can cause too many cells to transfer to the other parts of the agar plate, resulting in no pure cultures.

Improper zigzag technique could result in the same outcome.

Improper sterilization and aseptic techniques can contaminate the agar with other organisms

Question 8

What are the different elements for the colony characterization of “size” in agar plates?

Answer 8

Pinpoint, small, moderate, and large

Question 9

What are the different elements for the colony characterization of “form” in agar plates?

Answer 9

Circular, irregular, filamentous, rhizoid

Question 10

What are the different elements for the colony characterization of “pigmentation” in agar plates?

Answer 10

Any color the colony has. If it has no color, it is transparent.

Question 11

What are the different elements for the colony characterization of “margin” in agar plates?

Answer 11

Entire, lobate, undulate, serrate, and filamentous

Question 12

What are the different elements for the colony characterization of “elevation” in agar plates?

Answer 12

Flat, raised, convex, and umbonate

Question 13

What are the five colony characterizations for agar plates?