There are more than 5,000 known species of bacteria, with new ones constantly being discovered. Familiar species of bacteria include: E.coli, Salmonella, Bacillus.

Bacteria prefer moist conditions and can live in a wide range of temperatures. Most cannot grow at low pH (i.e. in acid conditions).

In the right conditions of warmth, acidity and moisture they can multiply very fast, producing millions of cells in a few hours. Some bacteria form spores which are resistant to drying and heating. When conditions become favourable again, they germinate and an active cell is released.

• spheres
• rods
• spirals
• commas.

They can be found as single cells, in pairs, chains or clusters.

A bacterial cell has a wall which maintains its shape and protects it. Some bacteria can move. Usually they use flagella, which are like little corkscrews. These rotate from the base like a ship’s propeller. The flagella may be distributed randomly over the whole cell surface, in groups or singly.

Some bacteria have numerous fringe-like projections called fimbriae which enable them to stick to each other. Other bacteria produce a sticky substance around the cell wall. This provides protection and helps them to stick to substrates, as well as each other.