Under optimal conditions, Escherichia coli has an approximate generation time of 20 minutes.
Generation time is the period required for a bacterial population to double, not necessarily the time needed for one individual cell to become visibly larger. In a nutrient-rich laboratory medium with suitable temperature, pH, oxygen, and aeration, E. coli can divide rapidly enough to double its population about every 20 minutes.
This speed makes E. coli an exceptionally useful model organism. A single cell can produce a large population in a relatively short experiment, allowing researchers to study genetics, metabolism, mutation, and gene expression. Its rapid growth also helped make it a standard host for recombinant-DNA technology and the production of some biological products.
The figure is an approximation, not a universal constant. E. coli grows more slowly when nutrients are limited, temperatures are unfavorable, waste accumulates, or oxygen transfer is poor. The 20-minute value therefore describes favorable laboratory conditions. It is also different from a pathogen’s doubling time inside a human body, where immune defenses and competition strongly change the environment.