APPENDIX 3O Gram Staining

  1. Richard Coico

Published Online: 1 MAY 2001

DOI: 10.1002/0471142735.ima03os23

Current Protocols in Immunology

Current Protocols in Immunology

How to Cite

Coico, R. 2001. Gram Staining. Current Protocols in Immunology. 23:3O:A.3O.1–A.3O.2.

Author Information

  1. CUNY Medical School, New York, New York

Publication History

  1. Published Online: 1 MAY 2001
  2. Published Print: JUN 1995


Named after Hans Christian Gram who developed the method in 1884, the Gram stain allows one to distinguish between Gram-positive and Gram-negative bacteria on the basis of differential staining with a crystal violet-iodine complex and a safranin counterstain. The cell walls of Gram-positive organisms retain this complex after treatment with alcohol and appear purple, whereas gram-negative organisms decolorize following such treatment and appear pink. The method described here is useful for assessing bacterial contamination of tissue culture samples or for examining the Gram stain status and morphological features of bacteria isolated from mixed or isolated bacterial cultures.