Microorganisms that cause diseases are often called germs.
Some diseases, like chickenpox, are caused by viruses. Diseases caused by viruses usually spread easily from one person to another.
Uncooked foods (especially meat) can contain bacteria. The bacteria are killed when the food is cooked properly. But if you eat food that has not been cooked properly, the bacteria may survive and make you feel very ill.
Bacteria left in your mouth by not brushing your teeth properly can cause a tooth infection. Bacteria left in your mouth could also cause an infection in your ear.
Mould is a type of microorganism that grows on decaying food. It can make you ill if you eat it.
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