Obtaining a Pure Culture from Isolated Colonies: Part 4
Introduction
Previously, it was found that the culture had been contaminated by a yellow bacteria that outgrew the Deinococcus radiodurans. It was suspected that the contamination came from an outside source, like the air from not keeping the inoculation loop properly under the flame. Other suspicions are that the tube was used and not properly cleaned so the bacteria invaded the culture from within.
To determine if the culture broth, within the tube, was contaminated or if it was just the agar plate that was contaminated, a new agar dish was prepared with the cultured broth and incubated for 5 days.
Materials & Procedure
The materials that were used for this analysis were as follows: a disposable inoculation loop, to reduce the chance of contamination, a P200 pipette, 50μL of the cultured broth that is suspected of contamination, a new agar plate, and an incubator set at 27° celsius.
First, with the agar plate ready for streaking, take the P200 pipette and draw 50μL of the cultured broth out of the tube. Then, carefully, dispense the broth onto the agar plate. Be sure to cover the plate quickly to avoid further contamination. Next, remove the disposable inoculation loop from the package. Take out the but the end that you will not be used to streak the plate to avoid contamination. Since this is an evaluation of the source of contamination, a formal streaking method is not necessary, open the agar plate and spread the culture all over the plate. Then place the plate in the incubator for the desired time period.
Results
After the incubation period, it was discovered that the cultured broth, within the tube, is in fact contaminated. This could have occurred from using a previously used to that was not properly cleaned or the top was removed from the tube which allowed contaminates to enter into the broth from the air. As it can be seen in the photograph above, the bacteria that has contaminated the Deinococcous radiodurans culture is bright yellow. There are still small colonies of D. radiodurans visible in certain areas on the dish but the other bacteria has almost completely colonized the agar plate.
Any thoughts as to what you co-cultured? Think about shape/color/conditions, etc.
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