You are given a milk sample You pipet out 11 mL into a 99 mL

You are given a milk sample. You pipet out 11 mL into a 99 mL peptone water bottle and further pipet out 1 mL from here into another 99 mL peptone water bottle. From that, you pipet out 1 mL and 0.1 mL into petri plates, respectively. What are the different dilutions that you plated?

Solution

Answer: 1/10 and 1/1000

First dilution:

Fold Dilution = (Stock volume)/(Stock volume + diluent)

Fold Dilution=11/(11 + 99) =1/10

Second dilution:

Fold Dilution=1/(1 + 99) =1/100

Final dilution = 1/10 x 1/100 = 1/1000