Question

A 0.1 dilution is performed on a culture of bacteria in order to perform viable plate counts. From the dilution, *0.1 mL* of solution is plated on solid media, and 218 colonies of bacteria grow on the petri dish. Assuming each colony came from a single bacterium, how many bacteria are in a single mL of the original culture? Express your answer to two decimal places using exponential notation.

Answer 1

The correct answer will be 2.18e4. Since 0.1 mL of solution contain 218 bacetria (As each colony came from single bacterium), 1 mL of solution contain 2180 bacterium. But this 1 mL of solution is obtained by 0.1 dilution (diluted the volume 10 times). It means the original solution concentration was 2180 X 10 = 21800. Thus the concentration of original culture was 21800 bacteria per mL.

This 21800 can be sintifically notated in the exponential form as follows:

21800 = 2.18 X 10⁴ = 2.18E4 or 2.18e4