Bacterial culture. View of petri dishes containing bacterial cultures. These petri dishes are filled with different coloured agar nutrient media on which bacteria are grown. Lines of bacteria have grown on the orange agar where they were streaked. This involves running a platinum wire loop that has been placed in contact with a bacterial culture over the agar. By heating the loop, each successive set of streaked lines leaves fewer bacteria, until round colonies form around single bacteria, as at the upper left of the orange agar. This technique is used to isolate particular strains of bacteria, which may then be incubated and grown in pure form.