C. Determine the CFU/mL of the original culture CFU/mL of diluted culture\" Dilu
ID: 150683 • Letter: C
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C. Determine the CFU/mL of the original culture CFU/mL of diluted culture" Dilution factor- /079 CFU/mL of original culture 3. If you needed to make a 100-fold dilution of a 0.1 mL bacterial culture, how much water should you add? 4. I counted 91 colonies on a plate inoculated with 100 microliters of a bacterial culture that was diluted 1,000,000-fold. How many colony forming units (CFUs) per mililiter are in the original culture? A. How many colonies would you expect to count on a plate inoculated with 100 microliters of a 10,000,000-fold dilution of the same original culture?Explanation / Answer
An easy formula to remember is
Dilution factor = Final volume(voume of culture + volume of diluent)/ volume of culture.
For a 100 fold dilution, Dilution factor is 100.
We have been given a volume of 0.1 mL.
putting the values in the formula,
100 = Final volume/ 0.1
10 = Final volume
10 = 0.1 + volume of diluent
0.9 mL = volume of diluent. (water)
4. volume of culture = 100 microliters. (100 microliters contains 91 colonies)
dilution factor = 1000000
1000000 = 100 microliters/ volume of original culture
volume of original culture = 100 microliters/1000000 = 10-4 microliters.
10-4 microliters of the original solution will also contain the same number of colony forming units as 100 microliters of the solution used = 91.
if 10-4 microliters give rise to 91 colonies, 1 microliter will give rise to 91/10-4 colonies.
1 mL = 1000 microliters.
1 microliter can form 91/10-4 colonies.
1000 microliters will have (91/10-4) x 1000 colonies.
91 x 107 colony forming units.
A. Dilution factor = 10,000,000
final volume = 100 microliters.
Applying the formula,
10,000,000 = 100 miroliters/ volume of original culture
volume of original culture = 100/10,000,000 microliters = 10-5 microliters.
Number of colony forming units in 1 microliter of original solution = 91/10-4
The number of colony forming units in 10-5 microliters of the original culture = (91/10-4) x 10-5 = 9.1.
you would find 9 colonies on the plate.
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