5.5: Review Questions
- Page ID
- 52341
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1. Why do we report bacterial counts as CFUs/mL?
2. A viable plate count was performed on a river sample. Using the table below, how many bacteria were present in the original river sample?
| Dilution | Amount plated | Number of colonies counted |
| 10-4 | 1.0mL | 310 |
| 10-5 | 1.0mL | 28 |
| 10-6 | 1.0mL | 7 |
2. How would you prepare a series of dilutions to get a final dilution of 10-10? outline each step.
3. When determining the number of bacteria from a sample using a viable plant count, why do you often have to do a 'serial' dilution of the sample first? Why don't you just plate out 1ml or 0.1ml of the sample on a spread plate?
4. Why is it called a "viable" plate count? what does that mean?