Microbiologist how-to

How to Perform a Gram Stain

Gram stains classify bacteria.

Updated By the Career Education Institute Curriculum Team
Quick answer

Gram stains classify bacteria. In short: prepare; apply; apply, then complete the remaining steps below.

Step by step

  1. Prepare and heat-fix a smear.

  2. Apply crystal violet.

  3. Apply iodine.

  4. Decolorize with alcohol.

  5. Counterstain with safranin.

  6. Examine under oil immersion.

Safety reminders for microbiologists

  • Follow biosafety level procedures
  • Wear PPE
  • Autoclave waste
  • Report exposures

Pathogen · Culture · Gram stain · CFU · Sterility test · Endotoxin: see the full microbiologist glossary.

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