1.14: Gram Stain Assignment
Name: _______________
Data and Observations
| Organism | color | Gram Reaction | Drawing |
Morphology and Arrangement |
Instructor Initials |
Post Lab Questions
- Explain the major differences between the Gram positive and the Gram negative cell wall.
2. What are the 4 major steps in Gram Staining and what is the role of each reagent?
A student divides a slide in half and places a mixed culture smear of E. coli and S. epidermidis on one side and a pure culture smear of an unknown microbe on the other. They Gram stain the slide and begin their observations by looking at the mixed smear under oil immersion. Evaluate the student’s Gram staining technique when the following results are observed. Explain what the student may have done wrong. If they also observe the unknown smear on the same slide, are their results likely to be accurate?
3. Both the rods and the cocci appear purple.
4. You can only find rods and they are all pink.
5. What is wrong with putting an unknown organism and the control mixed culture smear on different slides?
6. Why would a health care provider be interested in knowing the Gram reaction of a pathogenic bacterium?
7. Instead of the usual control organisms, you use Bacillus cereus , a Gram + rod, and Moraxella catarrhalis , a Gram – coccus. If stained correctly, what result do you expect to see?
If a student performs the perfect Gram stain except for the following mistakes, what result (color) would you expect to see if the cells were Gram negative? Gram positive?
8. The student skipped the iodine step.
9. The student left the safranin on for an extra 15 seconds.
10. The student delayed rinsing the Gram’s Decolorizer off the slide for a minute.
11. Methylene blue was used instead of safranin.
12. The student switched crystal violet and the safranin.