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Bacterial cultures. Gloved hand places a petri dish with a bacterial culture back onto a petri dish stack. These petri dishes are filled with different coloured agar nutrient media on which bacteria are grown. Lines of bacteria can be seen growing on the upper dishes 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. This technique is used to isolate particular strains of bacteria, which may then be incubated and grown in pure form.
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