Sometimes organisms cannot be separated because there may be an extremely motile organism present that is capable of even moving over solid media and contaminating separate colonies. When this happens, you will see a film of growth overlaying the isolated colonies-- an organism that exhibits this strong motility is referred to as a "swarmer". Proteus sp. are notorious for swarming. Special media must then be used to inhibit the swarming activity so that the organisms may be isolated into pure cultures.