Ten grams of hamburger were added to 90 ml of sterile buffer.

This was mixed well in a blender. One-tenth of a ml of this slurry

was added to 9.9 ml of sterile buffer. After thorough mixing, this

suspension was further diluted by a 1/100 dilution followed by a

1/10 dilution. One-tenth of a ml of this final dilution was plated

on agar plates. After incubation, 52 colonies were present. How

many colony-forming units were present in the total 10 gram sample

of hamburger?

5.2 * 10 ⁹ cfus

Explanation:

Using the dilution factors

0.1 ml of the final dilution has 52 colonies

1 ml will have approximately 520 colonies

10 ml of the final sample will have 5200 colonies

at 1 / 100 dilution

1 ml of the sample will have 5200 colonies

100 ml of the sample will have 520000 colonies

1 ml of the 0.1 ml + 9.9 ml has 520000 colonies

10 ml will have 5200000

at the second stage of the dilution

0.1 ml of the slurry had 5200000 colonies

1 ml will have 52000000 colonies

10 ml will have 520000000 colonies

100 ml of the initial sample (10 grams + 90 ml) = 5200000000 colonies =

5.2 * 10 ⁹ cfu