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How to Streak Bacteria on Agar Plates

Step 1:

Distinguish between a fresh plate and your bacterial or yeast sample.

  • Hold plates up to a bright background, and pan back and forth watching the glare on the agar
  • Bacteria looks like a cloudy film unevenly dispersed over the surface
  • Your fresh plate should be almost clear with a slight tint.

Bacteriaexample.jpg

 

 

 

Step 2: 

Retrieve bacteria with inoculating loop

  • Hold loop parallel to plate surface
  • Gently glide over bacterial colonies trying to gather and group them on the loop.

*DO NOT PRESS TOO HARD OR LOOP WILL BREAK AGAR*

  • A milky goo will be visible on the loop if performed correctly

retrievebacteria.jpg

 

Step 3:

Apply bacteria to fresh plate by spreading

  • Hold loop with bacterial sample parallel to fresh plate
  • Gently rub loop across surface spreading bacteria thinly throughout
  • Flip loop on other side or even gently drag edges across plate if visible bacteria still needs to be delivered.
  • You should be able to see the lines you made on the surface when you hold the plate like the test you did in Step 1.

 

 

streakbacteria.jpg