What is the principle behind the streak plate method?

The streak plate method relies on the principle of dilution and is a quick way to isolate bacteria for qualitative analysis. The goal is to obtain fewer colonies by spreading a small amount of culture on an agar plate. The spreading of the sample is done over a solid culture medium using a sterile tool like an inoculating loop. Starting from one edge of a sterile petri dish, the sample is streaked in various specific patterns over the agar surface; the initial culture gets spread thinly, separating individual cells. This gradual spreading helps to dilute the sample permitting bacterial cells to form distinct colonies which can be quantified as colony-forming units (CFUs) typically with a distance of a few millimeters between them. Upon incubation, these CFUs grow into distinct, well-separated colonies. This method helps in obtaining a pure culture and observing visual characteristics of the microorganism.