Page 91 - MNUmicrobiology practical 2025

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

Purpose of streaking

• To produce isolated colonies of an organism (mostly bacteria) on an agar plate. This

is useful when we need to separate organisms in a mixed culture (to purify/isolate

particular strain from contaminants) or when we need to study the colony

morphology of an organism.

• To identify the organism: biochemical tests to identify bacteria are only valid when

performed on pure cultures

Preparation of a Streak Plate (3 phases)

1 Loosen the top of the test tube containing the inoculum (Microorganism)

2 Hold the loop in the right hand.

3 Flame the loop and allow to cool.

4 Lift the test tube containing the inoculum
with the left hand.
5 Remove the lid/cotton wool plug of the test
tube with the little finger of the left hand.

General Microbiology & Immunology (PM 401) Practical note Page 80