Question

how can you tell that colonies on a plate are pure or from a mixed culture?

Answer 1

To examine whether the colony is from pure or mixed culture , you will need to examine the colonies with incident light through the transparent lid. Lid should be left on otherwise it is certain that the plates will be contaminated. If the culture is pure colonies should be distinguishable by size, shape , opacity and texture of colonies. If two colonies overlap and still can be distinguished then atleast 2 species are present. Colonies usually have a fairly simple uniform texture. If an area resembles like mosaic then the culture has more than one species. To confirm whether the culture is pure or not gram staining can be done from young cultures (less than 18 hrs). If the culture is mixed pure culture can be obtainef from the culture by performing three way dilution streak on a fresh plate.