Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to gram-negative bacteria, which cannot hold the crystal violet stain. Instead they take up the counterstain (safranin or fuchsine) and appear red or pink.
Gram-positive Bacillus anthracis bacteria (purple rods) in cerebrospinal fluid sample. The other cells are white blood cells.
Diagram of bacterial cell walls
The difference is caused by the cell wall structure. Gram-positive organisms have thick peptidoglycan layer. This protects them, so they do not need rigid cell walls. On the other hand, gram-negative bacteria have thin, insignificant peptidoglycan layers, so they do need rigid cell walls for support and protection.
Related pages
Other websites
- 3D structures of proteins associated with plasma membrane of Gram-positive bacteria
- 3D structures of proteins associated with outer membrane of Gram-positive bacteria
- Gram Staining Procedure and Images Archived 2012-02-22 at the Wayback Machine
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