Question
Asked Sep 19, 2019
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Plating 0.1 mL of a sample diluted by a factor of 10^(-3) produced 43 colonies. What was the original concentration (OCD) in the undiluted sample?

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Expert Answer

Step 1

The question asks the original concentration (OCD) is to be identified in an undiluted sample.

Dilution factor is defined as the ratio of the volume of the original solution (concentrated) to the volume of the absolute solution (dilute). It also means the ratio of V1 (original solution) to V2 (absolute solution).

Step 2

A colony-forming unit or CFU in microbiology is a unit that is used to determine the number of fungal cells or viable bacteria in a sample.

Given:

43 colonies are formed by plating 0.1 mL of a sample that is diluted with 10-3 factor.

The calculation of the bacterial cell number (or CFU per gram or milliliter) of a sample is done by dividing the plate count or the number of colonies on plate by the dilution factor. It is given on the white board:

Therefore, 1 mL of the original sample has 4.3 x 104 CFU.

CFU in1.0mL of 103 dilution = 43
Total CFU in original sample=Dilution factor
Plate count
43
103
=43000
or 4.3x103
1mL (original sample)= 4.3 x 10 CFU
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CFU in1.0mL of 103 dilution = 43 Total CFU in original sample=Dilution factor Plate count 43 103 =43000 or 4.3x103 1mL (original sample)= 4.3 x 10 CFU

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Step 3

Original cell density is known as OCD.

OCD can b...

Number of cells
Celldensity in the sample =
The original solution (permL)
4.3 x10 CFU
1 mL
- 4.3 x104 CFU/mL
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Number of cells Celldensity in the sample = The original solution (permL) 4.3 x10 CFU 1 mL - 4.3 x104 CFU/mL

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