Bacteria usually increase in number by dividing down the middle and splitting into two. Before dividing, the bacteria must make enough protein and DNA for two complete progeny cells. When these cells mature, they will in turn divide so that the number of bacteria doubles each generation.

As bacteria can divide as often as once every 15 minutes, one single bacterium can lead to a vast population after 24 hours. The following animation shows how a single bacterium will divide:

Not all bacteria are harmful 

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