Bacterial culture streaking allows bacteria to reproduce
on a culture medium in a controlled environment. The process involves spreading bacteria
across an agar plate and allowing them to incubate at a certain temperature for a period of time. Bacterial streaking can be used to identify and isolate pure bacterial colonies from a mixed population. Microbiologists use bacterial and other microbial culture streaking methods to identify microorganisms and to diagnose infection.
Time Required: 5 minutes
- While wearing gloves, sterilize an inoculating loop by placing it at an angle over a flame. The loop should turn orange before you remove it from the flame. A sterile toothpick may be substituted for the inoculating loop. Do not place toothpicks over a flame.
- Remove the lid from a culture plate containing the desired microorganism.
- Cool the inoculating loop by stabbing it into the agar in a spot that does not contain a bacterial colony.
- Pick a colony and scrape off a little of the bacteria using the loop. Be sure to close the lid.
- Using a new agar plate, lift the lid just enough to insert the loop.
- Streak the loop containing the bacteria at the top end of the agar plate moving in a zig-zag horizontal pattern until 1/3 of the plate is covered.
- Sterilize the loop again in the flame and cool it at the edge of the agar away from the bacteria in the plate that you just streaked.
- Rotate the plate about 60 degrees and spread the bacteria from the end of the first streak into a second area using the same motion in step 6.
- Sterilize the loop again using the procedure in step 7.
- Rotate the plate about 60 degrees and spread the bacteria from the end of the second streak into a new area in the same pattern.
- Sterilize the loop again.
- Replace the lid and invert the plate. Incubate the plate overnight at 37 degrees Celsius (98.6 degrees Fahrenheit).
- You should see bacterial cells growing in streaks and in isolated areas.
- When sterilizing the inoculating loop, make sure that the entire loop turns orange before using on the agar plates.
- When streaking the agar with the loop, be sure to keep the loop horizontal and only streak the surface of the agar.
- If using sterile toothpicks, use a new toothpick when performing each new streak. Throw all used toothpicks away.
What You Need
- Culture plate with microorganisms
- Inoculating loop or sterile toothpicks
- Agar plates
- Bunsen burner or another flame producing instrument