|back to protocols| The cells being plated are sandwiched
between layers of cell-free agar. The submerged cells grow into
smaller colonies and many more colonies can be counted per plate
(I've been able to distinguish over 1000 yeast colonies per
plate using this method--Jgritton 14:46, 22 Aug 2005 (EDT)). In
addition by avoiding the use of a spreader you can eliminate the
error due to cells sticking to your spreader. The result is more
accurate estimates of cell numbers in a sample. - Prepare petri
plates with 0.4 cm of base agar medium. - LB (or other nutrient)
with 1.2% agar for bacteria - YPD (or other nutrient) with 2%
agar for yeast - Prepare 0.7% agar medium (soft agar medium) -
Warm small test tubes to 45 C and add 3 mL of soft agar medium.
- Pipette sample to be plated onto inside rim of test tube. -
Immediately pour soft agar onto the base agar, pouring over the
pipetted sample. - Swirl plate to spread sample/agar mix and
allow to set - Pipette or pour 2 mL of soft agar onto plate and
swirl to sprea