Some bacteria manufacture and absorb their own food, while others must consume substances like living organisms or decaying material through their cell walls. Bacteria break down food in a process called respiration, which for some strains of bacteria requires oxygen to complete.
Many types of bacteria are able to eat a variety of things like milk, meat, oil and gas. Some bacteria live in the digestive tracts of humans and other animals and assist the body by helping to digest food and eating other, harmful bacteria. Escherichia coli, more commonly known as E. coli, is one bacteria that lives in the human body and survives by digesting food, absorbing some of the nutrients and releasing vitamin K. The harmful version of the E. coli bacteria causes people to become sick when ingested.
In order to eat, some bacteria absorb food through their cell walls. Many are autotrophs, meaning they make their own food using things like sunlight, water and soil, similar to the photosynthesis method many plants use. They absorb the food they produce and release oxygen into the air.
Bacteria are also used to make food like cheeses and yogurt. They eat the milk sugars and convert them to lactic acid, with softer cheeses having more bacteria than hard cheese.