Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

What is the goal of streaking an agar plate?

1. Pure culture

2. Individual colonies

3. No growth of pathogens

4. Dense growth which covers the plate

The correct answer is: Individual colonies

The goal of streaking an agar plate is to isolate individual colonies from a mixed population of microorganisms. When a sample is streaked on the surface of the agar in a specific pattern, the idea is to dilute the sample across the plate to the point that individual cells will grow into distinct colonies. Each of these colonies originates from a single cell, allowing for the study of specific organisms in isolation, which is crucial for identifying and characterizing the microorganisms present in the original sample. Achieving individual colonies is essential in microbiology for various reasons, including the ability to perform further testing on specific organisms, as well as to confirm that a pure culture has been obtained. Pure cultures provide important insights into the characteristics, behavior, and pathogenicity of specific microbes. The other options relate to different aspects of microbiological growth and control but do not accurately represent the primary goal of the streaking technique itself. For example, while obtaining a pure culture is a desired outcome of the streaking process, it is done primarily by the isolation of individual colonies first. Similarly, while controlling for pathogens or seeking dense growth might be important in certain contexts, they do not capture the foundational objective of the streaking method.