Stains & CD markers
Gram stain
Copyright: 2003-2024, PathologyOutlines.com, Inc.
PubMed Search: Gram stain[title]
Gram stain
Author: Nat Pernick, M.D.
Last author update: 1 September 2013
Last staff update: 2 July 2021
Copyright: 2003-2024, PathologyOutlines.com, Inc.
PubMed Search: Gram stain[title]
Cite this page: Pernick N. Gram stain. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/stainsgramstain.html. Accessed November 27th, 2024.
Definition / general
- Stain to detect and differentiate bacteria
Method:
- Apply crystal violet, then iodine, then decolorize by alcohol/acetone, then counterstain by safranin/fuchsin
- Gram positive bacteria retain the crystal violet-iodine complex after decolorization, are not counterstained, and appear purple
- Gram negative bacteria have a different cell wall structure, don’t retain the crystal violet-iodine complex after decolorization, and so are counterstained by safranin/fuchsin and appear pink/red
Paraffin sections:
- Use neutral red instead of safranin; gram negative organisms usually stain poorly because their bacterial wall lipid is removed in tissue processing
- Note: with hematoxylin and eosin staining on paraffin sections, bacteria appear as blue rods or cocci regardless of gram reaction; colonies appear as fuzzy blue clusters
- Rapid diagnostic strategy for bronchioalveolar lavage samples consists of Gram stain and bacterial ATP assay (Arch Pathol Lab Med 2005;129:78)
- Not suitable for burn wound surfaces (Arch Pathol Lab Med 2003;127:1485)
Microscopic (histologic) images
Images hosted on other servers:
Gram positive tissue sections
Bacillus anthracis in CSF
Lactobacillus osteomyelitis
Mycobacterium abscessus (soft tissue)
Additional references
