Bacteria are made up of just one cell
Bacteria are single-cell organisms. Some bacteria need oxygen to survive and others do not. Some love the heat, while others prefer a cold environment. Well-known examples of bacteria include salmonella and staphylococcus bacteria.
Most bacteria aren't dangerous for humans. Many of them even live on or in our body and help us to stay healthy. For instance, lactic acid bacteria in the bowel help us to digest food. Other bacteria help the immune system by fighting germs. Some bacteria are also needed in order to produce certain types of food, like yogurt, sauerkraut or cheese.
Less than 1% of all bacteria cause diseases – but this is just a rough estimate because there are no exact numbers. Tuberculosis, for instance, is caused by bacteria. Bacterial infections can be treated with antibiotics. These are medicines that kill the bacteria or at least stop them from multiplying.
Many other infections – including diarrhea, colds or tonsillitis – can also be caused by bacteria, but they are usually caused by viruses. Antibiotics aren't effective against viruses. So it's not a good idea to start using antibiotics too soon if you're not sure that it's a bacterial infection.