Dilution Series
You performed the following dilution series on a culture of Escherichia coli:
1 ml of the original culture to 99 ml broth
then 1 ml cell suspension to 9 ml broth
then 2 ml to 8 ml broth
then 0.1 ml to a culture plate
The next day, you count 52 colonies on the plate. What was the concentration of the original culture? (Hint: Drawing the dilution series may help.)
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Solution Preview
Whenever you get a wordy dilution problem like this one, it helps to draw out the dilution series so you can better visualize what is going on.
1 ml of the original culture to 99 ml broth
-- This is a 1:100 dilution
(1 ml is being added to 100 ml total, where total = amount added + amount already in the flask)
then 1 ml cell suspension to 9 ml ...
Solution Summary
The expert examines working with serial dilutions.