4. A student receives a solution of virus that has been diluted 1000 times (10 f

Question

4. A student receives a solution of virus that has been diluted 1000 times (10 from their lab instructor. They perform a 1:100 (102) dilution of this virus and plate 0.1mL of it onto a lawn of E coli. The next day they count 52 plaques on the plate. What is the pfu/mL of the original stock? 5. A researcher purifies a virus and wants to determine how much virus she has isolated. She takes her virus preparation and makes a 1:10,000 dilution of it. Then she performs a dilution series of the diluted virus. She prepares a dilution series of 3, 1:10 dilutions of her already diluted virus, 10", 10 and 10-3. She takes 100??of each tube from her dilution series and performs a plaque assay. The 101 plate has 2 plaques, the 102 plate has 50 and the 103 dilution has 350. Use these data to determine pfu/mL. Draw a picture if you are confused. 2

Explanation / Answer

4. plaque forming unit/ml or pfu/ml= number of plaques/ (dilution factor X volume)

Volume=0.1ml

number of plaques=52

here the original stock has been diluted 1000 times first and 100 times second which will be 100000 times or 105 times dilution in total. so the dilution factor is 10-5   .

= 52/(10-5 X 0.1ml)= 5.2 X10 -7 pfu/ml

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