Fundamentals of Microbiology

2.5.2 Generation Time

Bacterial numbers increase exponentially. The population will double in number during a specific length of time. The time required for a cell to divide is called the generation time or doubling time. For example, a culture tube is inoculated with one bacterium that divides every 20 minutes. The population would be 2 after 20 min, 4 cells after 40 minutes and so on. The increase in population is always 2ⁿ where n is the number of generations.

∴ After 6 generations the number of cells will be:

Population = 2⁶ = 64

After 20 generations = 2²⁰ = 1,048,576

This can be expressed as Nt = N0 x 2ⁿ

Nt = the population at time ‘t’

N0 = the initial number

                                                                         log Nt – log N0

n = number of generation in time ‘t’   n = -----------------------

                                                                               log 2