You are given a yeast culture of concentration 6 x 10^11 cfu/ml. You are asked t
ID: 81606 • Letter: Y
Question
You are given a yeast culture of concentration 6 x 10^11 cfu/ml. You are asked to make a 2.5 x 10-8 dilution from this stock culture. The volumes in your tube(s) should not exceed 10 ml and the volumes you pipette should not be less than 0.1 ml. (i) What is the CDF for this dilution? (ii) Given your volume constraints, can you do this dilution in a single step? If yes, show me how, skip questions (iii) and (iv), and answer question (v). If no, answer questions (iii), (iv), and (v). (iii) If no, demonstrate (draw or grid out) how you would set up the dilution. For each step, indicate in an orderly fashion the following information: V2, V1, diluent volume, DF and dilution for each step, CDF and C-Dilution upto that step, and yeast concentration at that step. (iv) Is this a serial dilution or a dilution series? (v) What volume should you plate from the 2.5 x 10-8 dilution to get 270 colonies?
Explanation / Answer
You are given a yeast culture of concentration 6 x 10^11 cfu/ml. You are asked to make a 2.5 x 10-8 dilution from this stock culture. The volumes in your tube(s) should not exceed 10 ml and the volumes you pipette should not be less than 0.1 ml.
(i) What is the CDF for this dilution?
=1/2.5 x 10^-8= 40000000=4x10^7
(ii) Given your volume constraints, can you do this dilution in a single step? If yes, show me how, skip questions
No, because the large CDF means that I would need to pipet 2.5 x 10^-8 ml into a tube that contains 10 – 2.5 x 10^-7ml, volumes that are impossible to measure accurately
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(iii) and (iv), and answer question (v). If no, answer questions (iii), (iv), and (v). (iii) If no, demonstrate (draw or grid out) how you would set up the dilution. For each step, indicate in an orderly fashion the following information: V2, V1, diluent volume, DF and dilution for each step, CDF and C-Dilution upto that step, and yeast concentration at that step.
first I would break up the CDF into smaller units that can accommodate the volume limits.
For example
=4 x 10^7= 4 x 10 x 10 x 10 x 10 x 10 x 10 x 10
Tube 1
Tube 2
Tube 3
Tube 4
Tube 5
V1or transfer volume
0.1 ml
0.1 ml
0.1 ml
1 ml
1.8 ml
Diluent in the tube
9.9 ml
9.9 ml
9.9 ml
9 ml
8.2 ml
V2 in the tube
10 ml
10 ml
10 ml
10 ml
10 ml
DF from the previous tube to this one
10 ml/0.1ml= 100
10 ml/0.1ml= 100
10ml/0.1ml =100
10 ml/1 ml =10
10 ml/1.8 ml= 5.5
CDF up to this tube
1 x 10^2
1 x 10^4
1 x 10^6
1 x 10^7
4 x 10^7
Concentration cfu/ml
1.8 x 1010cfu/ml/100 =1.8 x 10^8
1.8 x 10^8cfu/ml/100
=1.8 x 10^6
1.8 x 10^4cfu/ml
1.8 x 10^3cfu/ml
4x10^7
Tube 1
Tube 2
Tube 3
Tube 4
Tube 5
V1or transfer volume
0.1 ml
0.1 ml
0.1 ml
1 ml
1.8 ml
Diluent in the tube
9.9 ml
9.9 ml
9.9 ml
9 ml
8.2 ml
V2 in the tube
10 ml
10 ml
10 ml
10 ml
10 ml
DF from the previous tube to this one
10 ml/0.1ml= 100
10 ml/0.1ml= 100
10ml/0.1ml =100
10 ml/1 ml =10
10 ml/1.8 ml= 5.5
CDF up to this tube
1 x 10^2
1 x 10^4
1 x 10^6
1 x 10^7
4 x 10^7
Concentration cfu/ml
1.8 x 1010cfu/ml/100 =1.8 x 10^8
1.8 x 10^8cfu/ml/100
=1.8 x 10^6
1.8 x 10^4cfu/ml
1.8 x 10^3cfu/ml
4x10^7
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