Most colonies on streak plates grow from isolated colony-forming units. on rare occasions, however,

Most colonies on streak plates grow from isolated colony-forming units. on rare occasions, however, a colony can be a mixture of two different organisms. if a culture is started from this colony (thinking it’s pure), correct identification will be next to impossible because the extra organism could confound the identifying test results. how could you verify the purity of a colony? if you found the colony to be a mixture of organisms, what could you do to purify it?