Summary
A staining technique that divides bacteria into Gram-positive and Gram-negative by cell wall structure.
In depth
Gram-positive bacteria have a thick peptidoglycan layer that retains crystal violet and stain purple; Gram-negative have a thin layer plus an outer membrane that loses the stain and appear pink after the safranin counterstain. The difference guides antibiotic choice since the outer membrane is a barrier.
Developed by Hans Christian Gram in 1884.
Steps: crystal violet, iodine, alcohol wash, safranin. Over-decolourising makes Gram-positives look negative. Old cultures may stain variably.
Common mistake: Gram status refers to cell wall type, not shape.
Frequently asked questions
What is Gram Staining?
A staining technique that divides bacteria into Gram-positive and Gram-negative by cell wall structure.
Which area of biology covers Gram Staining, and how advanced is it?
Gram Staining is one of the 54 topics in Microbiology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Bacterial Cell Wall, Conjugation, Probiotics.
Can you give an example of Gram Staining?
Streptococcus is Gram-positive and E. coli is Gram-negative.
What should I learn before Gram Staining?
Gram Staining is a Beginner topic, so no earlier topic is required. Other Beginner topics in Microbiology that pair well with it include Microorganisms, Bacteria, Archaea.
What topics are related to Gram Staining?
The closest topics to Gram Staining are Bacterial Cell Wall, Conjugation, Probiotics, Archaea. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Gram Staining?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Gram Staining. To practise the whole of Microbiology, use the Microbiology quiz.
How is Gram Staining different from Bacterial Cell Wall?
Gram Staining: A staining technique that divides bacteria into Gram-positive and Gram-negative by cell wall structure. Bacterial Cell Wall: Peptidoglycan gives bacteria shape and strength; Gram-negative species add an outer membrane. Read both side by side and note what each one explains.
What is a common mistake about Gram Staining?
Gram status refers to cell wall type, not shape.
How should I study Gram Staining step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Bacterial Cell Wall and explain the difference aloud. Finally, take the Microbiology quiz and come back to this page for any question you miss.