This document discusses techniques for obtaining a pure culture from a mixed culture sample. It explains that a pure culture contains only one type of microorganism, while a mixed culture contains multiple types. The most common laboratory methods for isolating microbes are the streak plate method and pour plate method. Both rely on diluting bacterial cells to a point where single colonies can grow from individual cells. The streak plate method involves transferring a sample to an agar plate using a sterilized loop and streaking the inoculum in sections to separate individual colonies.

1. Pure culture technique
Prepared by
Samira fattah
Assis. Lec.
College of health sciences-HMU
Lab 7

2. • Pure culture:
is a culture that contains a single known
species or type of Microorganism.
Aim:
To identify the bacterial pathogens.

3. • Mixed culture need to be separate.

4. • The most commonly used method in the laboratory for
isolating microbes is:
- The streak plate
and to a lesser extent
- The pour plate.
• Both methods rely on dilution of bacterial cells in a sample to
the point at which a single cell can divide giving rise to a single
pure colony.

5. Streak Plate technique
(Quadrant Streak, loop dilution)

7. Types of streaking

8. Pour plate technique
• one loopful from the mixed culture
is transferred between 3 tubes
contain nutrient agar(wormed to
50C degree) .
• then poured to plates and allowed
to solidify and then incubated.
melted nutrient agar

9. Lab Exercise
Streak plate method
What is required for
pure culture?
• Sterile apparatus
• Aseptic technique
• Appropriate media

10. Step 1:Do the initial inoculation then FLAME the
loop, let cool about 15 seconds.

11. Step 2: Use the sterile cooled loop and draw
over the agar surface in the first section, flame
and cool.

12. Step 3: Use the sterile cooled loop and draw of the agar surface
in the second section. Note that you overlap with the first
section a few times. Flame the loop and allow to cool.

13. Step 4. Use the sterile cooled loop and draw of the agar surface
in the third section. Again overlap with the second section
only. Now flame loop.

14. Step5. place the plate in incubator.

15. Isolated Colonies