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Tiny Staphylococcus epidermis, a bacteria that lives on the skin, seen at the microscope.

Bacteria are one of the three main groups of living beings (with the other being archaea and eucaryots). Bacteria have usually only one (or only a few) tiny cell, which makes them very little : bacteria can't be seen with just the eye, and will need a microscope : they are called microorganisms.

Bacteria are very abundant on every part of Earth : they live in water, on the soil, and even on and inside the other (greater) living beings : for example, your own body contains ten times more bacteria than human cells and, if put together, all the bacteria in your body would weigh about 1 kg!

Don't worry, most bacteria are harmless, and even better, many of them are very useful! Some of them protect us from diseases or help us to feed, etc.

Some bacteria are responsible of disease: they are rarer, but better known, this is why we often believe that bacteria are harmful.

Some examples[edit | edit source]

(most of bacteria don't have a common name, just a scientific name)

  • the Escherischia coli (E Coli) : it lives in our guts : its is the most common bacteria in the human gut. It is mostly harmless, and might help with digestion, but overgrowth can be dangerous & make people very sick.
  • the Lactobacillus : it lives in yogurt, and milk products. It is bred there, because it helps turning the milk into yogurt : it is called a ferment. Other kind of bacteria are also used as ferment, and transform different kind of food.
  • Cyanobacteria : they live in water, and are part of the phytoplancton. They use the light of the Sun to thrive : this is photosynthesis. Cyanobacteria in large numbers, often turn the water green or black.
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