Question

Example An otherwise typical bacterial cell increases from one cell to 256 cells in 10 hours. What is the generation time of this organism? Example: Escherichia coli has a doubling time of 20 minutes. If there are 5 cells at the beginning of the experiment, how many will there be in 3 hours? Example You perform a serial dilution and determine that the original number of cells in your sample was 12,000. How many bacteria will be present in 12 hours if the generation time is 15 minutes (assume unlimited food and clean environment)? Example 10 You determine that a coconut cream pie has 3 million (3 x 10 Staph. aureus cells in it. You estimate that the food preparer did not wash his hands and probably inoculated the cream with 500 Staph. aureus. He also forgot to refrigerate it. If the pie was made 6 hours ago, how many generations have occurred? How long is each generation? Example 11 Using the generation time from problem 2, how many bacteria would be present after 8 hours at room temperature? Example 12 Let's say that flesh eating Strep. pyogenes divides every 10 minutes at body temperature. You fall down and scrape your knee and get infected with 5 Strep. pyogenes cells. After 4 hours, without medical intervention, how many bacteria will be ravaging your body? Let's say that for every 1 million bacteria, a centimeter of flesh is consumed. After 4 hours, how much tissue would be lost? Are you still alive and would you want to be?

Answer 1

7) N=N₀2^t

N= number of cells after t generations=256

N₀= number of cells present initially=1

t= number of generations=?

N=N₀2^t

256=1*2^t

2^t=256

taking log on both sides

t log2= log (256)

t= log (256)/log2

= 8

so after 8 generations, there will be 256 cells, and 8 generations took 10 hours

so the time of generation= time required to grow from 1 cell to 256 cells/number of generations took to make 256 cells

= 10 hours/8

= 1.25 hours

so the generation time= 1.25 hours