4.3.3: True/False

1. It’s feasible to count the number of colonies on a plate if they are going to exceed 500.

2. The dilution factor of a particular bacterial culture made when 30 microliters (µL) is added to 270 µL of sterile broth is the same dilution factor as when 10 milliliters (mL) is added to 90 mL of sterile broth.

3. A petri dish with the abbreviation “TNTC” marked on it indicates that there are fewer than 30 colonies present.

4. Plates should not be counted if they have more than 100 colonies present on them.

5. Viable plate counts are the most accurate method of counting bacteria, because only viable (living) cells are counted.

6. The direct microscopic count allows the observer to distinguish living cells from dead cells.

7. A sample is drawn into the Petroff-Hausser counting chamber by capillary action.

8. Every cell in the counting chamber must be counted in order to determine the number of cells present.

9. To determine the number of cells in the original sample, the average cell count is multiplied only by the dilution factor of the chamber.

10. A single colony forming unit may consist of more than one bacterial cell.

11. An undiluted sample may be plated directly, since the colonies would still be isolated enough to count.