Cognitive Apprenticeship (L05)

Question 1

How is bacterial concentration determined?

Answer 1

Count the number of isolated colonies formed on each plate
Select plates with manageable number of colonies (30-300) for counting
- plates with >300 (TNTC)
- plates with <30 (TFTC)

Question 2

What is the definition of a pure culture and a mixed culture?

Answer 2

Pure culture: a culture containing a single species of organism
Mixed culture: a culture containing 2/more types or organisms

Question 3

What are the steps for streak plating?

Answer 3

1. Pick up sterile disposable inoculating loop
2. Pick up the agar plate with the colony of interest
3. Use the inoculating loop to touch the isolated colony
4. Gently streak it on the new agar plate
5. Turn the agar plate anti-clockwise
6. Use the same loop, perform streaking from the first streak
7. Use the same loop, perform streaking from the second streak
8. With the same loop, complete the streaking with a final streak
9. Close the inoculated agar plate immediately and discard the inoculating loop

Question 4

What is the purpose of streak plating?

Answer 4

To obtain single isolate pure colonies

Question 5

What are the steps for inoculating a liquid media?

Answer 5

1. Pick up a sterile inoculating loop
2. Pick up the agar plate with the colony of interest
3. Use the inoculating loop to touch the isolated colony
4. Pick up the tube with fresh broth, flame, open, flame
5. Dislodge the inoculum into the broth, by gently scrapping on the wall of the tube
6. Flame, close, flame and replace the back to the rack
7. Discard the inoculating loop