A pure culture consists of entirely one strain of organism and is important for studying a particular microbe. Solid media are particularly useful for the isolation of bacteria to obtain such cultures.

The standard method for obtaining a pure bacterial culture is the streak plate method. In this technique, an inoculating loop is used to streak out a drop of bacterial suspension on a solid agar plate in such a way that it becomes progressively more dilute.

After proper incubation at an appropriate temperature, visible bacterial colonies are developed near the end of the streak. Colonies are formed because all the progeny stay in the same place and the movement of daughter cells is not possible on the solid surface.

An alternative method is the pour-plate method. Here, the original microbial sample is diluted several times to dilute the population sufficiently. Small volumes of each dilution are poured on the bottom of a Petri plate.

Subsequently, the melted medium with agar is poured onto the Petri plates and mixed gently with a circular motion. After incubation, the isolated cells grow into colonies, which can be used to establish pure cultures.