2.3.4: Exercise #8 Lab Wrap-Up

Answer the following questions:

1. Why is the Gram stain considered a differential stain?
2. How does the age of a culture affect the Gram stain reaction? What is the optimum age for a valid Gram reaction?
3. Which step in the Gram stain procedure is most prone to error? If done incorrectly, how might that step affect the end result?
4. A wound culture is taken from a post-surgical patient showing signs of infection. The Gram stain shows purple clusters of round cells.
   1. what is the likely Gram reaction and morphology of this organism?
   2. How might this result guide the medical team's initial treatment decisions while waiting for full identification and sensitivity results?
5. Place steps of the Gram stain in the proper order by placing the appropriate number 1-4 under the images.

   

   

   

   

   Credit: Sherry Smith

6. For each image indicate whether the result is gram-positive or gram-negative?

   

7. Describe how each type of cell will appear in the following scenarios in which the Gram stain was incorrectly performed.
   1. The decolorizer step was omitted.
      1. Gram positive
      2. Gram negative
   2. The mordant was eliminated.
      1. Gram positive
      2. Gram negative
   3. The counter-stain step was forgotten.
      1. Gram positive
      2. Gram negative