Page 60 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

Isolation Technique

• In nature microbial cultures are mixed

• Identification relies upon isolating individual colonies

• Testing requires pure cultures

The Streak-Plate Method (plating out)

• Colonies are masses of offspring from an individual cell

therefore streaking attempts to separate individual cells.

• An isolated colony, one that is not touching any other colonies,

is assumed to be a pure culture.

• The streak-plate method is the simplest and most commonly

used technique for isolating bacteria

• An original inoculum containing a mixture of bacteria is spread into

4 quadrants on solid media.

• The goal is to reduce the number of bacteria in each subsequent

quadrant.

Colony Morphology Characteristics

- Colony color

- Type of hemolysis

- Form

- Elevation

- Margin

General Microbiology & Immunology (PM 401) theoretical handbook Page 49