Staphylococcus aureus is grown in heart-infusion broth at 37°C. If you start exponential phase with 100 cells, and after 90 minutes you have 800 cells, what is the generation time for S. aureus?

30 minutes

Explanation:

Bacteria reproduce by binary fission, a process by which one parent cell divides to form 2 progeny cells. Because one cell produces 2 progeny cells, bacteria are said to undergo exponential (logarithmic) growth.

As in the case of staphylococcus aureus, we start with 100 cells, and after 90 minutes number becomes 800 that means, firstly the cells doubled (100 x 2 = 200) after 30 minutes. Again after 30 minutes they doubled (200 x 2 = 400) and again after 30 minutes they doubled (400 x 2 = 800). So in 90 minutes 100 cells became 800 cells.

Hence the generation time for S. aureus is 30 minutes.