The basic principle of the streaking plate method is dilution by physically spreading bacteria across the agar surface, aiming to obtain isolated colonies.
The streaking plate technique, a fundamental method in microbiology, relies on progressively diluting a bacterial sample over the surface of a solidified agar medium in a Petri dish. As the bacteria are spread, the cell density decreases. Ideally, this process results in individual bacterial cells being deposited far enough apart on the agar surface that, upon incubation, they will grow into visibly separated colonies. Each of these isolated colonies theoretically originates from a single bacterial cell, allowing for the creation of a pure culture.
Here's a breakdown:
- Dilution: The initial inoculum is diluted with each streak. The successive streaks pick up fewer and fewer bacteria.
- Isolation: The goal is to separate individual bacterial cells on the agar surface.
- Colony Formation: During incubation, each isolated cell multiplies to form a visible colony.
- Pure Culture: Because each colony ideally arises from a single cell, it represents a pure culture of that particular bacterium.
The method relies on a specific streaking pattern to achieve this dilution. Common patterns include the quadrant streak, the T-streak, and the continuous streak. The specific pattern used may vary depending on the density of the original sample.
