Bacterial Dilution Problems
Before completing these problems, review Appendix B: Bacterial Dilutions and a Foolproof
Way to Figure Them Out.
For these problems, assume each bacterial cell will give rise to one colony.
1. (1 pt) One mL of a sample was mixed with 99 mL of sterile diluent. (This is a gen-
eral term that refers to any liquid medium that is used to dilute a sample.) One mL
of this was transferred to nutrient agar. After incubation for 48 hours, 241 colonies
were present on the plate. How many bacteria were present per mL of the original
sample?