Technique
Add 1ml aliquots of a suitable series of decimal dilutions to empty 9cm Petri dishes. Two dishes are used for each dilution. Then add to each dish approximately 15ml of medium cooled to 50°C. Mix gently, turning the plates three times clockwise and three times counter clockwise.
Allow the medium to gel then turn the petri dishes upside down and incubate them for 5 days at 22 ± 2°C.