# How to calculate generation time and number of generations of bacteria?

What is Generation time in Microbiology?

Generation time is the time required for a bacterial cell to grow and divide or the time required for a population of cells to double in number.

The generation time of E.coli in glucose salts is 17 minutes. That means if initial number is 10, to become 20, 17 minutes is required.

Let us work out a problem.

? if 100 bacteria multiply to produce a population of 3.28 × 106 cells in 7 hours, then What is the generation time of this bacterium?

Generation time (min/generation) = 60 minutes X number of hours

number of generations

Step 1: Find out the number of generations.

No. of generations= log No. of cells at the end of reproduction- log No of cells initially

log 2

Log 2 is used in the formula as each bacterial cell produces 2 offspring on each division.

Step 2: Substitute the values.

Final No. of cells at the end of reproduction=3.28 × 106 cells

Initial No. of cells =100

No. of generations=log (3.28 x 106) - log (100)/ log2

=6.515-2/0.30102

=4.515/0.30102

=14.99 =15 generations

Now we know the number of generations.

Step 3 Find out generation time by substituting the values.

No. of hours: 7 hours (given in the question)

No. of generations: 15 hours (from the previous step)

Generation time (min/generation) = 60 minutes X number of hours

number of generations

Generation time (min/gen) = 60 minx7hrs =28 min/generation

15

Thank you