Discussion:
Using a Serial Dilution to Count Bacteria in a Sample
Consider the following dilution scheme:
A. 1oomL lake water
B. 5mL lake water into 45 mL diluent 0.1 ml - colonies TNTC
C. 1mL from B into 9ml diluent 0.1 ml - colonies 425
D. 0.5mL from C into 4.5 mL diluent 0.1 ml - colonies 58
E. 2mL from D into 19mL diluent 0.1 ml - colonies 12
F. 0.1mL from E into 0.9 mL diluent 0.1 ml - colonies 1
a. What dilution is achieved by adding 2mL of incoulum to 19mL of a diluent?
b. Would you expect any change in the answer of the above problem if the firat dilution was made by adding 1 mL of sample to 9 mL of diluent? Why or why not?
c. What are the total number of CFU's in the entire 100mL amount of the original lake water sample?