Experiment 3 Post-Lab Questions
1. What color are the Gram-positive bacteria after Gram staining? Gram-negative bacteria? (5 points)
Gram-positive bacteria appear as dark purple or blue due to retaining the primary dye (Crystal Violet) in the cell wall.
Gram-negative bacteria appear as red or pink due to decolorizing to accept the counterstain (Safranin).
2. What different characteristic(s) exist between the two groups that account for the different staining conditions? (5 points)
Gram-positive bacteria are stained purple, and gram-negative bacteria stain as pink. They are two distinct morphological groups of bacteria.
3. Why was the Gram iodine added to the Gram staining procedure? (5 points)
Gram iodine is added as a mordant to stabilize the crystal violet iodine complex so that the dye cannot be removed easily.
4. Why is a counterstain (safranin) added to the Gram staining procedure? (5 points)
A counterstain is used to help identify gram-negative bacteria. Gram-negative bacteria lose the crystal violet and stain red.
5. What are the advantages of performing a Gram stain vs. a simple stain for visualizing bacteria? (5 points)
Gram stain contains two or more different stains and can differentiate the species of bacteria into two main groups (gram-positive and gram-negative) by looking at the color of cells (pink or purple). Simple stain involves single stain and it is used to easily determine cell shape, size, and arrangement.
6. Using either a textbook or a reputable online resource, research some of the typical characteristics of bacteria, and discuss why it might be important for a researcher or a hospital technician to be able to differentiate between Gram-positive and Gram-negative bacteria. (5 points)
7. Did you experience any technical difficulties or atypical results during this experiment? If so, what happened, and how could you avoid these issues in the future? (5 points)