Plate Count : Answer toPractice
Problem #1.
The correct dilutions
are shown on the tubes and plates above.
The formula to be
used is:
the number of CFUs per ml of sample
=
the number of colonies (30-300)
X
the dilution factor of the plate
counted
-
First choose the correct plate to
count, that is, one having between 30 and 300 colonies.
- The correct plate is the one
having 63 colonies on the 1/1,000,000 or 10-6
dilution. (6.3 X 101 in scientific notation.)
- Multiply 63 by the dilution factor
of that plate.
- Since the dilution factor
is 1/1,000,000 or 10-6, the dilution
factor or inverse is 1,000,000 or 106.
-
63 X 1,000,000
= 63,000,000 CFUs per ml. (6.3 X 101 X 106 = 6.3 X 107
in scientific notation.)
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to Lab 4
Microbiology Laboratory Manual by Gary E. Kaiser, PhD, Professor of Microbiology
is licensed under a Creative Commons Attribution 4.0 International License.
Last updated: August, 2017