Question

You perform a spread plate to determine the bacterial population in a batch liquid media. You plate 0.1ml of a 10-5 dilution. You incubate the plate and count 10 colonies (cfu). What is the bacterial population in cfu/ml of the stock (undiluted) culture? 10 million colonies 1 million colonies 100 million colonies

Answer 1

Answer: 10 million colonies

The volume of media used is 0.1ml and the concentration diluted to 10^-5, so the actual volume used would be: 0.1ml * 10^-5= 1ml * 10^-6

The media shows 10 colonies. The number of colonies per volume would be: 10 cfu/ (1ml * 10^-6)= 10* 10^6 cfu/ml= 10 million cfu/ml