Here's why:

* Isolation: Before you can study a bacterium, you need to isolate it from any other organisms that might be present. A pure culture ensures you're working with only one type of bacteria.

* Accuracy: Identifying a bacterium based on its characteristics requires a sample that isn't contaminated with other species.

* Further Testing: Once a pure culture is obtained, you can then proceed with various tests like:

* Microscopy: To observe the bacterium's morphology (shape, arrangement) and staining properties.

* Biochemical tests: To assess the bacterium's metabolic capabilities.

* Molecular techniques: To analyze the bacterium's DNA or RNA, often for species-specific identification.

How to obtain a pure culture:

* Streak Plate Method: A common technique where a sample is streaked across an agar plate, diluting the bacteria to the point where individual colonies can grow.

* Enrichment Techniques: Using specific media that favors the growth of the target bacterium.

* Selective Media: Using media that inhibits the growth of other bacteria, allowing the target bacterium to grow.

Remember: The method used to obtain a pure culture will depend on the specific sample and the suspected type of bacteria.