EXERCISE 3

 

Pure Culture Techniques –Streak Plates

 

 

Supplies required: Cultures of Micrococcus luteus, Enterococcus faecalis, and Chromobacterium violaceum, 3 tryptic soy agar plates.

Protocol:

 

PERIOD 1: (The streak plate technique is illustrated at:

http://www-micro.msb.le.ac.uk/video/labvid.html

Click on Aseptic Technique.)

 

1.         Label the bottom of a T.S. agar plate as instructed earlier, and with the name

C. violaceum.

 

2.         Aseptically remove a loopful of C. violaceum culture as instructed earlier

            for making a smear. Spread the organisms over a small area near the edge of the plate.

Be careful NOT to dig into the agar.

 

3.         Flame and cool your loop. Make 4-6 streaks from area containing the organisms into the adjacent area. Stay fairly close to the edge of the plate.

 

4.         Flame and cool your loop. Make 4-6 streaks from the second area into the adjacent area.

 

5.         Flame and cool your loop again. Make as many streaks as you can from the third area into the adjacent area using the remainder of the plate as much as possible. Make sure you do not cross into other streak lines in this last step. Reflame your loop before

            setting it down.

 

6.         Repeat the experiment with a second plate using M. luteus and a third plate using

            E. faecalis.

 

After 48 hours your plates will be refrigerated.

 

PERIOD 2:

 

Check your streak plates for well-isolated colonies. Can you resolve individual colonies on your

streak plate? A properly streaked plate should have numerous well-isolated colonies from which

restreaking could be done.