Gram stain

Stain a control slide and see how each Gram reagent affects the bacterial envelope. Compare crystal violet retention in thick and thin cell walls. Then work out what went wrong on three slides.

What to know first
Specimen Collection, Transport, and Primary Processing in Microbiology
How long it takes
About 12 minutes.
What's free
The watch-through and the control slide open without an account. A free account opens every case.

Stain the control slideWorking at the bench needs JavaScript.

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Gram stain

Control slide

Meniscus lot GS-2611

Left spot
S. aureus ATCC 25923
Right spot
E. coli ATCC 25922

Methanol-fixed · thin smear

Primary stain

Crystal violet gets into every cell and stains them both purple.

Bench clock0 s / 60 s

Gram-positive wall

Gram-negative envelope

Thick peptidoglycanCross-bridges · teichoic acids
Membrane bilayer · cytoplasm

LPS · porins · outer membranePeriplasm · thin peptidoglycan
Inner membrane bilayer · cytoplasm