Streak (shown in Yellow).
Hold the plate as though you are going to "paint" the surface of the agar . If you are right-handed, hold the plate in your left hand, and the inoculating loop in your right - as through you would a paint brush. Hold the plate in your right hand, and inoculating loop in your left if you are left-handed.
Dip your inoculating loop (sterile swab, or sterile stick as shown in the above picture) into a broth culture, or touch it to the material you want to spread - an isoated colony or swab an area for which you want to quantitate the microbial species present.
Go back and forth a number of times in a small area of the Petrie plate. The goal is to spread your material completely over this inital area of the plate.
Streak (shown in Blue).
Sterilze your inoculating loop, or use a fresh, sterile inoculating stick or swab. Squelch it in an unused area of the agar before steaking to cool it. If you were to use the original, unsterile loop, you will not be diluting the individual microbes you plates in the first streak.
Pick up the plate and rotate it 1/4 of a turn to your left (if right-handed), or to your right (if left handed).
Run the loop through the previous streak 2-3 times, then draw it along 1/3 of the remaining plate, as shown by the blue line in the above image.
It's OK if you gouge a little bit of the agar, but with practice you should be able to streak cleanly across the surface.
Rotate the plate another 1/4 turn and sterilize your inoculating loop or take a fresh, sterile stick or swab. Squelch a heated inoculated loop it in an unused area of the agar before steaking to cool it.
Run the loop through the previous, secondary streak 2-3 times, and draw the streak over a remaining 1/3 of the plate, as shown.
Rotate the plate another 1/4 turn and sterilize the inoculating loop. Squelch a heated inoculated loop it in an unused area of the agar before steaking to cool it.
Run the loop through the previous tertiary streak 2 times and draw over the remaining free space in the plate, being careful not to contact the primary streak (yellow).
© 2005, Lynn Bry. All rights reserved.