Plate Count : Answer to Practice
The correct dilutions
are shown on the tubes and plates above.
The formula to be
the number of CFUs per ml of sample
the number of colonies (30-300)
the dilution factor of the plate
- 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
- 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.)
to Lab 4