Plate Count : Answer to Practice
Problem #2.
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 161 colonies on the 1/1,000,000 or 10-6
dilution.
- Multiply 161 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.
-
161 X 1,000,000
=161,000,000 CFUs per ml (1.61 X 108
in scientific notation.)
Return
to Lab 4