Your professor handed you a tube with an E. coli culture and asked you to prepar
ID: 147164 • Letter: Y
Question
Your professor handed you a tube with an E. coli culture and asked you to prepare a 101 dilution using 100 u of culture. How would you do this? 1. Your professor handed you a tube with 1 ml of an E.coli culture and asked you to prepare a 0.1, 0.01 and 0.001 dilutions using the full 1 ml volume. Explain how you would do this 2. 3. What would be the dilution if you add 5 ml to 45 ml of diluent? In addition, convert 5 ml and 45 ml to ul. Suppose you were instructed to add 20 ul to 0.98 ml of diluent but instead you added 2 . what was the intended dilution, and what was the actual dilution? 4. You plate 0.1 ml of a sample diluted by a factor of 1 x 101 and count 100 colonies. Calculate CFU/ml in the undiluted sample. Express the result using exponents 5. 6. Plating 200 ul of a sample diluted by a factor of 1 x 10* and count 100 colonies. Calculate CFU/ml in the undiluted sample? 7. You take 0.1 ml of an undiluted culture at 5 x 10 CFU/ml. You then add 4.90 ml of sterile diluent. What is the dilution and what is the final cell density (CFU/ml)? You have 20 1 of a sample and want to dilute the sam ple the 20 1 sample? Express the result in ml and 8. 100-fold. How much diluent do you have to add t 9. If the sample has 6.5 x 10* cFU/ml, how many colonies should be counted if you plate 100 ul from the dilution 1 x 10 10. The original concentration in a sample is 1.5 x 10 CFU/ml. What dilution should you prepare to obtair 11. You plate 200 ul of a sample diluted by a factor of 10s on a nutrient agar plate. After incubation you co 12. How many colonies would you count if you plate 100 1 of the sample in Question 11 instead of 200 ! countable colonies after plating 100 ul? 200 colonies. Calculate the CFU/ml in the undiluted sample.Explanation / Answer
Answer for Question 1 :
To obtain 10-4 dilution from 100L of culture we need to perform serial dilution. Serial dilution is the process for obtaining a dilute version of the original solution by mixing a fixed amount of the solution to a fixed amount of another solvent(usually distilled water while exceptions can be there). This follows a geometric progression pattern.
Here, we have only 100L of culture. To obtain 10-4 dilution we need to take 4 test tubes or vials. Each vial must contain 90L of distilled water. Let the vials be labelled as A,B,C and D.
In vial A : Add 10L of culture solution in the vial and mix thoroughly. So the volume now is 100L (90L distilled water + 10L culture solution). Thus the vial A contains 0.1 dilution.
In vial B : Add 10L of solution present in vial A and mix thoroughly. So the net volume in vial B is 100L and dilution is now 0.01. Note that the 10L of culture solution taken in vial A is diluted twice till now.
In vial C : Add 10L of solution present in vial B and mix thoroughly. So the net volume in vial C is 100L and dilution is now 0.001. Note that the 10L of culture solution taken in vial A is diluted thrice till now.
In vial D : Add 10L of solution present in vial C and mix thoroughly. So the net volume in vial D is 100L and dilution is now 0.0001. Note that the 10L of culture solution taken in vial A is diluted four times till now.
Thus we have obtained 10-4 dilution from 100L of culture.
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