Sometimes, bacteria swim or float freely in liquids – in the water in your tap, in juice left sitting on the counter, or, if a person has a blood infection, even in human blood. Swimming allows bacteria to move around to find food, or move away from things they do not like, such as bright sunlight, or cells from the human body that want to eat bacteria. But, most bacteria would rather sit still than swim around. Sitting still takes less energy, and bacteria that sit in the right spot can wait for food to come to them. Sitting still is the first step in making a bacterial biofilm. The first bacterium that sits still might be joined by others, or it might reproduce and make many more bacteria that are copies of itself. When more and more bacteria get together, they start to make sticky substances called extracellular polymeric substances that they cover themselves with. This sticky community of bacteria is called a biofilm. The bacteria in a biofilm live happily eating whatever food comes along and can communicate with each other by releasing special molecules. Biofilms are very common.

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