Streak for Isolation

From a culture of mixed or concentrated bacteria, dilute the sample by streaking on an agar plate so that colonies arising from individual cells can be isolated.

1. sterilize a bacterial loop by flaming
   
2. allow the loop to cool slightly and gather a small sample of either bacterial culture or a small scraping of a frozen bacterial stock onto the loop
   
   • for frozen stocks, do not allow the stock to thaw
     
3. streak the loop across the top of a bacterial agar plate in three parallel lines
   
   • the lines should be fairly close together
     
   • streak using the wide part of the loop, not the edge of the loop
     
4. flame sterilize the loop and cool by stabbing a clean part of the agar plate
   
5. make three new parallel streaks starting by going across the last part of the previous three streaks and continuing onto a clean part of the plate
   
   • repeat the last two steps three or four times being careful to only contact the immediately previous streaks and not earlier streaks
     
6. grow at 37C overnight
   

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Comments

• there are many procedures that will work, but this procedure is quick, easy to perform and more reliable than most others