Table of contents

1. Introduction to Microbiology3h 22m
2. Disproving Spontaneous Generation1h 18m
3. Chemical Principles of Microbiology3h 38m
4. Water1h 28m
5. Molecules of Microbiology2h 23m
6. Cell Membrane & Transport3h 28m
7. Prokaryotic Cell Structures & Functions5h 52m
8. Eukaryotic Cell Structures & Functions2h 18m
9. Microscopes2h 46m
10. Dynamics of Microbial Growth4h 36m
11. Controlling Microbial Growth4h 10m
12. Microbial Metabolism5h 16m
13. Photosynthesis2h 31m
14. DNA Replication2h 25m
15. Central Dogma & Gene Regulation7h 14m
16. Microbial Genetics4h 44m
17. Biotechnology3h 0m
18. Viruses, Viroids, & Prions4h 56m
19. Innate Immunity7h 15m
20. Adaptive Immunity7h 14m
21. Principles of Disease6h 57m

9. Microscopes

Gram Stain

Microbiology

9. Microscopes

Gram Stain

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Multiple Choice

A scientists has a sample with two different species of bacteria. The first species is Staphylococcus aureus, a gram-positive bacterium. The second species is Escherichia coli, a gram-negative bacterium. The scientist gram-stains his sample of bacteria. What colors will the two species of bacteria be after staining?

Staphylococcus aureus:pink; Escherichia coli:purple.

Staphylococcus aureus:purple; Escherichia coli:pink.

Both Staphylococcus aureus and Escherichia coli will be purple.

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Verified step by step guidance

Understand the Gram staining process: Gram staining is a differential staining technique that distinguishes between Gram-positive and Gram-negative bacteria based on the composition of their cell walls.

Identify the characteristics of Gram-positive bacteria: Gram-positive bacteria, like Staphylococcus aureus, have a thick peptidoglycan layer in their cell walls, which retains the crystal violet stain, appearing purple under a microscope.

Identify the characteristics of Gram-negative bacteria: Gram-negative bacteria, like Escherichia coli, have a thinner peptidoglycan layer and an outer membrane. They do not retain the crystal violet stain after the alcohol decolorization step and instead take up the counterstain, safranin, appearing pink.

Apply the Gram staining steps: First, apply crystal violet stain to the sample, then add iodine, which forms a complex with the crystal violet. Next, use alcohol to decolorize the sample. Finally, apply safranin as a counterstain.

Determine the final colors: After the Gram staining process, Staphylococcus aureus will appear purple due to its thick peptidoglycan layer retaining the crystal violet stain, while Escherichia coli will appear pink as it takes up the safranin counterstain after losing the crystal violet during decolorization.