Question

I diluted a cell culture by 100X, 100 X and 3X. If the original culture contained `4.76 × 10^6"` cells/mL, how many colonies should I expect to see on the plate?

Answer 1

You can expect at most 16 colonies.

Explanation:

The dilution factor is `100 × 100 × 3 = 3 ×10^4`.

So the concentration after the serial dilutions is

`(4.74× 10^6"cells")/"1 mL" × 1/(3 × 10^4)` = 158 cells/mL

Then in the solution you apply to the plate, you have

0.1 mL × `"158 cells"/"1 mL"` = 16 cells

You should expect to see at most 16 colonies on the plate.

For an excellent video on how to calculate serial dilutions, see