PUBLISHED : Monday, 19 April, 2010, 12:00am
UPDATED : Monday, 19 April, 2010, 12:00am


About 4 billion years ago, the first life to appear on Earth was very simple. The first living things on our planet were tiny, single-celled organisms. Scientists have a special word for this kind of life: prokaryotes (pro-KAR-ee-yo-tees). Many of these are bacteria.

We can't see them, but bacteria are so common that they make up one of the three 'domains', or empires, of life. Your body is home to about 1 trillion bacteria. A trillion is 1,000,000,000,000 - about 150 times the number of people on the planet.

Not just nasty germs

Bacteria get a lot of bad press. Most people think of them as nasty. Some of them are. But with 10 times as many of them on and in our bodies as cells, they can't be all bad. Of course, it is true that bad bacteria in food can poison us. Everyone experiences eating something 'bad' at some point. That's bacteria our body does not want.

But we also deliberately introduce bacteria and other organisms called yeasts to certain foods to transform them in a process called fermentation. We add types of bacteria to milk, for example, to make yoghurt or cheese. Kimchi or soy sauce would be impossible to make without bacteria. They even play a role in making chocolate: cocoa fruit must be fermented before their beans can be processed.

The baddies

Even though we need bacteria for wine and cheese and yogurt and many other delicious foods, there are bacteria we don't want in our food. Bacteria that make us sick are called pathogenic bacteria. One of the nastiest ones is the bacteria that causes anthrax. If it gets into the lungs, it almost always kills people.

A bacteria with a very long name causes pneumonia - Streptococcus pneumoniae. Another nasty bacteria you have probably heard of is E coli. Most E coli are harmless and we have them in our stomachs, although some cause food poisoning. E coli is a risk especially in ground- meat products. It often leads to recalls of supermarket products before lots of people get poisoned.

Interesting facts

Bacteria move around using one or more tail-like structures called flagella. They do not move very fast by our standards - around 0.0007km/h. But that is about 27 times their body length every second. If that were an adult human, it would be like running 100 metres per second.

Bacteria are everywhere. Some live in very high temperatures, in hot springs. Others live very deep in the sea, more than a kilometre down at very high pressures. Some species at the North and South poles can survive in temperatures of minus 85 degrees Celsius.

now do this

1 There are about ... bacteria in and on our bodies.

a. 1 million

b. 1 trillion

c. 1 billion

2 We need 'good' bacteria to make ...

a. yogurt

b. milk

c. orange juice

3 A bacteria that is bad for us is called ...

a. E coli

b. pneumoniae

c. pathogenic


April 12