Quantitation of Microorganisms

Question 1

What range of colonies are considered accurate for counting?

Answer 1

30-300

Question 2

What is the formula for the number of bacteria in a colony (also works for original colony)? (CFU/mL)

Answer 2

of colonies x (1/total dilution)

Question 3

If the infection dose for a bacteria species grown on a plate is 10,000 bacteria, how many infectious doses are present in a colony containing 760,000,000 bacteria?

Answer 3

760,000,000 / 10,000 = 76,000 infectious doses

Question 4

If 57 colonies are on a 10-6 plate, how many bacteria were on the 10-5 plate?

Answer 4

57 x 10 = 570 colonies