Which technique is primarily used to isolate individual colonies from a mixed culture?

The streak plate technique is predominantly utilized to isolate individual colonies from a mixed culture because it effectively separates different species of microbes across a solid agar surface. This method involves using a sterile loop to spread a small amount of the mixed culture across the surface of the agar in a specific pattern. As the loop is sterilized and used to make successive streaks, the density of cells decreases, allowing individual cells to be deposited far apart from each other. As these cells grow and multiply, they form distinct colonies that can be differentiated based on their morphology.

In contrast, the spread plate technique distributes a diluted microbial sample over the surface of an agar plate using a sterile spreader, allowing for the enumeration of viable cells but not necessarily for effective isolation of individual colonies in a practical sense. The pour plate technique involves mixing a sample into molten agar and then allowing it to solidify, which can also lead to colony formation but is less effective for isolating colonies compared to the precision of the streak plate method. The filtration technique, while useful for isolating microbes based on size, does not provide the means to separate individual colonies directly on the culture medium. Thus, the streak plate technique stands out for its primary purpose of isolating individual colonies from a mixed culture.