CFU calculation Scenario 4 PDF

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CFU calculations SOIL SAMPLE WEIGHT = 2.3 g VOLUME OF BUFFER SUSPENTION = 10 ml 1. Select a suitable dilution and count the total number of colonies on the plate. Colonies counted = 117 102 cfu/plate 2.

cfu per plate = 1.17 x

The number counted in the previous step is the cfu in 100 µl of that particular dilution. How do we convert this back to the number in our original sample? Follow these steps:

(a) Calculate the cfu in 1 ml of the diluted sample. To do this, multiply the raw cfu count by 10. (remember, we only plated 100 µl of the dilution, which is 0.1 ml) dilution = 10-4

Cell concentration in diluted sample =

1.17 x 10 3

cfu / mL

(b) Calculate the cfu concentration in the original soil suspension. To do this, multiply the number from (a) above by the reciprocal of the dilution factor, i.e. if you used the 10 -4 sample for counting, then multiply by 104 (10,000).

Cell concentration in original soil suspension = cfu / mL

1.17 x 107

(c) Calculate the total cfu in your soil suspension by multiplying the number from (b) above by the suspension volume you used. This converts the cfu from a concentration to an absolute number.

Cell number in original soil suspension = cfu

1.17 x 10 8

(d) Calculate the number of cells per gram of soil by dividing the number from (c) above by the weight of soil (g) used in the experiment.

Practical 9 and Practical 10

Cell density in soil = gram

1.17x10 8

/2.3g = 5.09 x107

cfu /

Remember to present your final calculation in scientific notation i.e. 3.7 x108 cfu/g (not 370000000 cfu/g)

Practical 9 and Practical 10...