Bacteria in culture. Different media used to grow or store cultures of bacteria. At centre some Petri dishes are seen in which bacteria grow in agar. This is a mucilaginous carbohydrate that is used in the form of a gel as a microbiological support medium. Cryo-tubes are seen to the left of the Petri dishes; they are used to store strains of bacteria at low temperatures. Bacteria are placed in the little holes in the beads inside the tubes. To the right a selection of sealed glass ampoules is found. They contain freeze-dried samples of bacteria.