Isolation of colonies from a mixed culture (streak-plate technique) The purpose of this experiment is to learn how to isolate a culture by streaking. Being able to isolate a single organism is an extremely important aspect to working in a microbiology lab. In order to examine a specific organism on a petri dish, that organism must be isolated from the many other types of organisms that may be present. To do so, the aseptic technique, as well as properly streaking a petri dish must be employed. The goal of this experiment is to isolate an e. coli organism by transferring it from one petri dish to another. Incubate the petri dish inverted for 24 to 48 hours at 37 degrees c. An isolated sample of e. coli (right) and s. aureus (left) were the result of proper aseptic and streak-plating techniques.