gram stain lab

Gram Stain, Aseptic Technique, and Streak Plating

Materials and Methods:

Gram Stain:
A drop of water was placed on a clean microscope slide. An isolated colony of bacteria was picked up with an inoculating loop and swirled around in the water on the microscope slide. The slide was set aside until it was dry. It was then covered with methanol and set aside to dry to fix the bacteria to the slide. Then it was swiped 2-3 times through a flame to heat fix the bacteria to the slide even better. The slide was then covered with crystal violet for at least 1 minute before rinsing and blotting with bibulous paper again. The slide was then covered with gram iodine for 30 seconds before rinsing and blotting with bibulous paper. The bacteria on the slide were then decolorized with 5-12 drops ethanol (until the liquid turned clear) before rinsing and blotting with bibulous paper again. The slide was then covered with safranin for 1 minute and then it was rinsed with water and blotted with bibulous paper.

Gram Stain
When the gram stain slide was observed under oil emersion on a compound microscope, it was observed that all of the bacteria had the same uniform circular shape and were all in clusters that resembled grapes. Not all of the bacteria were the same color. Some sections of the slide had clumps of really pink bacteria while others kind of faded into slightly darker purple colors. The spots of color were quite irregular.

The circular shape of the bacteria that were observed to be in clusters like grapes exhibited the traits of cocci bacteria. The patchy fading colors of the bacteria observed on the gram-stained slide showed evidence of an error in the decolorization process with the ethanol. The ethanol was probably not spread evenly across the slide and some of the bacteria was not decolorized enough. Since all of the bacteria on the gram stain slide came from the same isolated colony, it was unlikely that the slide was contaminated and there were multiple types of bacteria on the slide. If the bacteria on the slide were decolorized properly, it is likely that they all would have appeared pink. This means that it can be concluded that the isolated colony that was picked up at the beginning of the gram stain procedure were gram-negative cocci-shaped bacteria.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License