Question

On Thursday night you are up late studying for your microbiology exam the next day (even though you know that cramming the night before is NOT the correct way to study for this class). Your lab partner stops by and the two of you decide to order a pepperoni pizza. By 1 A.M. you are exhausted. One piece of the pizza is left but you are too tired to wrap it up and put it in the refrigerator, so you leave it in the box on your desk and go to bed. While closing the lid of the box you sneeze and deposit 1000 Staphylococcus aureus cells onto the pizza. At room temperature this organism has a generation time of 30 minutes. In the morning you wake up, still exhausted, and realize you already late for your 8:30 A.M. class. Too late to get breakfast, you grab the left over pizza and rush to class. 1. How many Staphylococcus aureus cells are on the piece of pizza you ate in the morning?

(5) Time Approximate number of bacteria

2am

3am

4am

5am

6am

7am

8am

9am

Answer 1

G = t/n

t = time interval in hours or minutes

B = number of bacteria at the beginning of a time interval

b = number of bacteria at the end of the time interval

n = number of generations (number of times the cell population doubles during the time interval)

b = B x 2ⁿ

b = B x 2¹⁵

b = 1000 X 32768

= 3.28 X 10⁷

3.28 X 10⁷ numbers of Staphylococcus aureus cells are on the piece of pizza he ate in the morning.

2 am: 1000 X 4 = 4000 bacteria

3 am: 1000 X 16 = 16000 bacteria

4 am: 1000 X 64 = 64000 bacteria

5 am: 1000 X 256 = 2.56 X 10⁵ bacteria

6 am: 1000 X 1024 = 1.02 X 10⁶ bacteria

7 am: 1000 X 4096 = 4.09 X 10⁶ bacteria

8 am: 1000 X 16384 = 1.64 X 10⁷ bacteria

9 am: 1000 X 65536 = 6.55 X 10⁷ bacteria