Difference Between Gram-Positive and Gram-Negative Bacillus Written by WebMD Editorial Contributors Medically Reviewed by Sabrina Felson, MD on April 27, 2025 ...

Differences between gram-positive and gram-negative bacteria. All bacteria have a cell wall composed of mesh-like strands of ...

Gram-positive bacteria show blue or purple after Gram-staining in a laboratory test. They have thick cell walls. Gram-negative bacteria show pink or red on staining and have thin walls.

Differences between gram-positive and gram-negative bacteria All bacteria have a cell wall composed of mesh-like strands of a big molecule called peptidoglycan, which surrounds the cell membrane.