Gram Stain: How stains and counterstains work

Time to complete course: 12 min.

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About Gram Stain: How stains and counterstains work Virtual Lab Simulation

This short, targeted simulation is adapted from the full-length “The Gram Stain: Identify and differentiate bacteria” simulation.

Did you know that almost all 5 million-trillion-trillion bacteria in the world can be divided into Gram-negative or Gram-positive groups? Have you ever wondered how exactly the structural components of the cell wall get stained? Dive into the microscopic world and discover the colorful magic of Gram staining procedure!

Explore the bacterial cell wall structure

Compare and contrast the cell wall of Gram-positive and Gram-negative bacteria by diving into their microscopic samples and observing how the cell wall structures retain certain reagents during the experiment. Discover how the four reagents of the Gram stain interact with structural components of the cell wall to color the bacteria.       

Interpret given samples using a microscope 

Being able to tell the difference, you will use a light microscope to interpret the results of a given Gram stain. View the microscopic image on the computer screen, and remember to  apply immersion oil to increase magnification! Will you be able to identify the presence of bacteria?

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Have you ever wondered how the bacteria cell actually gets stained during Gram staining procedure? Dive into the world of microbiology with us! Discover how the cell retains a certain colour during the experiment and to differentiate it under the microscope!

Techniques in Lab

  • The Gram stain technique
  • Light microscopy

Learning Objectives

  • Relate the structure of bacterial cell envelopes to Gram stain outcomes
  • Differentiate the gram positive and gram negative bacteria under the microscope

Simulation Features

Length – 12 minutes
Accessibility mode – Available
Languages – English, French, German, Spanish, Italian

Examples of Related Standards


Microbiology related 1st year




Biology 1.3: Membrane Structure
Biology 6.3: Defence from infectious disease


Biology Unit 2: Cell structure and function

Screenshots of Gram Stain: How stains and counterstains work Virtual Lab Simulation


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