1. You have been given a tube of E. coli . You are asked to make 1 mL total volume of 10 ^-1 dilution of the bacterial culture. Explain how you would do this. Show all necessary calculations.

2.

1. You have bacteria at a concentration of 5 x 10 ⁸ CFU/mL.
2. You spread 1 mL of this sample on an agar plate to obtain isolated colonies.
3. How many colonies do you expect to find the next day after incubation at 37 ⁰ C?
4. Can you count these colonies?
5. Can you use this plate for determining concentration?

3. You have bacteria at a concentration of 1 x 10 ³ CFU/mL (in real life – you don’t know this, but we are just working on math skills here). You transfer 1 mL of this sample into 9 mL of water and then spread 1 mL on a plate of agar. How many colonies do you expect to find the next day after incubation at 37 ⁰ C? Can you count these colonies? Can you use this plate for determining concentration?

4. You take 0.05 mL of a culture of bacteria at a concentration of 4 x 10 ⁷ CFU/mL, and add 4.95 mL of water to it. What is the dilution that you have performed? What is the concentration of bacteria (CFU/mL) in the diluted culture?

5. You have diluted a sample by 1000 fold (1/1000) and plated 1 mL on an agar plate. You observe 55 colonies. What was the concentration of the original sample in CFU/mL?

6. A bacterial sample has a concentration of 3 x10 ⁷ CFU/mL. You make serial dilutions of 10 ^-3 followed by 10 ^-2 and 10 ^-1 dilutions. You finally plate 1 mL of the last dilution on an agar plate and incubate it at 37 ⁰ C. What is the total dilution?How many colonies do you expect to see on the plate?

Total dilution:

# of colonies expected on plate:

7. This time, you see 10 times fewer colonies than you had expected to see.What could have gone wrong? How will you fix this problem?

Answer rating: 100% (QA)

1 09ml of medium added to 01 ml of original Ecoli bacterial culture Explanation 10 raised to the minus 1 dilution is 1 part in 10 As the total volume ... View the full answer