Introduction to Microbes

What is a microbe?• Some living things are so small that we can only

see them with a microscope– These are called micro-organisms or microbes– They include:• Bacteria• Viruses• Fungi

Bacteria • Found everywhere – in the air, in the soil, in

water, inside living things• Some are useful but some cause diseases such

as pneumonia, scarlet fever, and tuberculosis• They are single-celled organisms with a cell

wall• Multiply very quickly• Affected by antibiotics

Viruses• Smallest microbe• Parasites – rely on another organism (the host) for

food and to reproduce• Not proper cells – have no nucleus nor cell

membrane; a strand of DNA wrapped in a protein coat

• NOT affected by antiobiotics• Cause diseases such as influenza, the common

cold, measles, chicken pox, and AIDS (HIV)

Fungi

• Larger than viruses• Plant-like but have no chlorophyll• Examples include yeast and mould• Can be helpful (yeast makes bread rise) and

harmful (athlete’s foot and ringworm)

Growing Microbes in the Lab

• Like all living things, microbes need food to get their energy

• We can grow them in the lab on a special jelly called agar in a Petri dish

• Agar jelly contains seaweed• If the bacteria are kept warm, they will

multiply very rapidly (bacteria can double in number in 20 minutes!)

6

41

3

2

5 Why are Steps 4 and

5 so important?

Practical – Growing Bacteria

• We will use a control–Needed so we can be sure of the cause; so

we can see the difference–Acts as a basis for comparison