The purpose of streak plate is to create isolated pockets of colonies derived from a single cell. The isolation allows the study of a genetically significant colony with reduced replication interference from other strains.
The three streak, T method, is the most widely used streak method. It was first used in 1961 and fully described in 1968, although streaking has been a part of lab science as far back as 1881. Another popular streak method is the quadrant method which uses four streaks. This method has been modified into a five streak method as well.
The three streak, T method, has some advantages over the five streak method. First, the three streak method better divides the streak plate into three distinct areas of concentration. The T method is also useful when examining a pristine inoculum.
The five streak method is better when the sample is tainted or subject to replication interference, but the T method will provide better colony isolation. The limited streaks of the T method reduces the chance for replication error and provides a larger area for single colonies to grow. In theory, the experimenter cannot be sure of the size the colony will grow to and should leave as much separation between isolation groups as possible to avoid cross-over contamination.