5.2: The Gram Stain Procedure
The Gram Stain Procedure
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The following activity will teach students how to complete a Gram Stain and identify bacteria based on their different cell wall properties. Read the following procedure carefully before starting the activity.
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Step 1: Prepare A Bacterial Smear
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Step 2: Heat Fixation
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| Procedure | |
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Step 3: Gram Staining
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Observation Results
General Questions
1. The Gram Stain is a differential stain used to observe cell wall structures. How are differential stains different to simple stains?
2. Describe the structure of the cell wall in Gram Positive and Gram Negative Bacteria.
3. You prepare a gram stain for a known gram positive species. When you observe your slide, all the cells are pink. What may have happened during your slide prep to produce this result?
4. After preparing your gram stain, you realize you never heat fixed the slide. What might your slide look like without heat fixation?
5. You prepare a gram stain for a known gram negative species. When you observe your slide, your results are gram variable (pink and purple calls are present). What can happen with the bacteria and slide prep to produce this result?
Health-Related Questions
1. How do Lactobacilli contribute to vaginal health?
2. What can lead to an overgrowth of G. vaginalis ?
3. A patient suffering from vaginal burning and itching submits a vaginal swab for microscopic analysis. After completing a gram stain, the sample contains a large population of purple rods and only a few pink cocci. Based on these results, would you diagnosis this patient with vaginosis caused by G. vaginalis ? Explain your answer.
Attributions
"Microbiology Laboratory Manual: Labs, 1.10 Gram Stain" by Dr. Rosanna Hartline, LibreTexts: Biology , West Hills College Lemoore is licensed under CC BY-NC-SA 4.0
"General Microbiology Lab Manual: Labs 3, Simple, Negative, and Gram Stain" by Nazzy Pakpour and Sharon Horgan , LibreTexts: Biology , Coastal State University, Easy Bay is licensed under CC BY-SA
"Microbiology Textbook: Chapter 2, How We See the Invisible World" by Openstax , Digital ISBN 13: 978-1-947172-23-4 is licensed under CC BY 4.0
Image Citations
Procedure Images Modified From:
- " Equipment - Wash bottle -- Smart-Servier " by Laboratoires Servier on "Creative Commons" is licensed under CC BY-SA 3.0 .
- "Microbiology Laboratory Manual: Labs, 1.10 Gram Stain" by Dr. Rosanna Hartline, LibreTexts: Biology , West Hills College Lemoore is licensed under CC BY-NC-SA 4.0