Final answer:
Isolated colonies for creating pure cultures and determining bacterial numbers can be acquired using serial dilution and plating techniques such as spread plate or streak plate methods.
Step-by-step explanation:
To obtain isolated colonies for creating pure cultures and determining bacterial numbers in a sample, the most effective method is serial dilution followed by plating techniques such as the spread plate or streak plate method. In serial dilution, the original bacterial sample is systematically diluted in a series of tubes or wells, with each dilution reducing the number of bacteria. The diluted samples are then plated on agar plates, and after incubation, individual bacteria grow into separate, visible colonies. These colonies can then be counted to estimate the number of bacteria in the original sample. This process ensures that each colony originated from a single bacterium, leading to a pure culture of that organism.