It’s a Numbers Game

Learn how bacteria grow.

Parents are usually 20-40 years older than their children.

A typical generation time for hamsters 🐹 can be as short as 6 weeks, for mosquitoes 🦟 10 days.

For E. coli bacteria 🦠, this only takes 20 minutes!

Bacteria multiply by dividing into two identical ‘daughter cells’. This means when you start with 1 bacterial cell and provide all the goodies it needs to grow (sugar, salt, water, some special nutrients like amino acids), after 20 minutes you’ll have 2 bacteria.

After another 20 minutes you’ll have 4 bacteria, after 20 more minutes you’ll have 8 bacteria.

The number of E. coli cells doubles every 20 minutes, which means bacteria can increase in number very quickly… Take a look at the graph and see what this means over long periods of time!

The number of E. coli cells doubles every 20 minutes, which means bacteria can increase in number very quickly… Take a look at the graph and see what this means over longer periods of time!

Growth of E. coli bacteria, starting with a single cell at 9:00 o'clock. The x-axis at the bottom shows the time, the y-axis on the left the number of bacterial cells. The way the graph gets steeper and steeper is called "exponential growth".

With time the tiny bacterium that you can’t see without a microscope grows into a lump of bacteria that form a visible spot, a ‘colony’, on an agar plate.

Each such bacterial colony originates from a single individual bacterium. This way you can quite easily count how many bacteria you had at the beginning of your experiment.

Now imagine you started an experiment and plated a single bacterium on an agar plate at 9:00 in the morning.

We already know now that at 10:00 you would have 8 bacteria. But how many would you have at 12:00, at 16:00, at 21:00? 🤔

How many would you have at 6:00 o’clock on the next morning, if the bacteria had sufficient space and nutrients to keep on dividing? ⏰


Try to see if you can answer the following questions correctly.

Click on the flags below to do a little Quiz:


➡️ Grow Your Own Microbes

Take a look at the bacteria that are on your skin and live in your mouth, ears and nose - and that sit on the dirty screen of your mobile phone.