Rationale: The plaque assay resulted in a contamination, so I will gram stain the contaminant in my control plate and the arthrobacter lawn in my plaque assay plate to see if it was arthrobacter contaminating my control plate.

Procedure:

1. Took loops and heated them to clear off contaminants. Pipetted 10μL of

   water onto two sections of a microscope slide.

2. Dragged loop through large culture on contaminated control plate and placed

   into the water. Repeated with arthrobacter lawn from plaque assay after

   heating the loop.

3. Let air dry then heat fixed the bacteria to the slide. Flooded slide with crystal

   violet dye and let sit for about 1 minute.

4. Rinsed off dye then flooded slide with Lugol’s Iodine and let sit for 1 minute

   and rinsed off.

5. Added a small amount of ethanol to slide and rocked around slide for about

   20-30 seconds. Then rinsed off.

6. Finally flooded with safranin dye and let sit for another minute then rinsed

   off and dried.

7. Observed under 1000x magnification using oil immersion.

Observations:
The contamination turned out to be a gram-positive bacilli bacterium. Whereas, the arthrobacter lawn looked more like a gram-negative cocci bacterium. This shows that the contaminant was, most likely, not from accidentally getting some of the arthrobacter onto the plate but instead a bacterium that may have fallen into the plate.

Image on the left is contaminant. Image on the right is arthrobacter.

Interpretations and Next Steps:
This means that we need to be extra carefully about not accidentally breathing on the plate or touching the inner parts of the lids of anything we use in class. Also, we should be more diligent about staying within the aseptic zone created by our flame. That way, the likelihood of something falling into our plate or top agar mixture is greatly reduced. Furthermore, we should try to be as quick as possible in order to minimize time that the plate is open to the air. For next steps, now that I have collected soil samples from saplings in Cameron park we can wash and run plaque assays on those. This time being more diligent about using aseptic technique so that this won’t happen again.