Final answer:
The streak plate method is the most commonly used technique to obtain a pure culture by isolating individual colonies derived from a single bacterial cell on an agar plate.
Step-by-step explanation:
The technique most commonly used to obtain a pure culture of bacteria is the streak plate method. This method involves diluting the bacteria by spreading them out on an agar plate surface using a specific pattern. The objective is to isolate individual bacterial cells that will grow into separate colonies, each originating from a single cell, ensuring that the culture is pure. Serial dilution is often performed before using the streak plate method to achieve an optimal concentration of cells on the plate.