How do streak plating and pour plating differ in technique and purpose?

• A. Pour plate never gives colony morphology
• B. Streak plate isolates individual colonies from a mixed culture on a surface; pour plate distributes cells into agar to count CFU and observe colony morphology within the medium.
• C. They are the same technique
• D. Streak plate yields CFU counts; pour plate isolates colonies

Answer: (B)

The key idea is how plating technique determines whether you isolate single colonies on a surface or count viable cells by embedding them in the medium. Streak plating uses a sterile loop to drag the sample across the agar surface in successive dilutions, which separates cells so that individual colonies form on the surface. This is ideal when you want a pure culture for identification and further testing, since isolated colonies can be picked and analyzed without contamination.

Pour plating disperses cells into molten agar, then the mixture is poured into a plate and allowed to solidify. The colonies develop within the agar, enabling you to count colony-forming units per milliliter and observe colony morphology inside the medium. This approach is used for quantitative enumeration and for studying colonies in a three-dimensional environment.

The statement that pour plates never show colony morphology is incorrect, because colonies can be observed within the agar. They are not the same technique, and streak plating is not used primarily for CFU counts—the pour plate is.