THE BEECHMONT CREST GUIDE TO BIOLOGICAL TERMS
BACTERIA CELL WALLS
Most bacteria are enclosed by cell walls of peptidoglycan--- a carbohydrate matrix that is crisscrossed with polypeptide units. (Many antibiotics-- like penicillin-- kill bacteria by interfering with the linking of these polypeptide units.)
Bacteria are classified according to how their walls appear when subjected to the Gram staining procedure.
The walls of gram-positive bacteria are thick, and consist of a single layer of cells. They retain the purple dye used during Gram staining.
Gram-negative bacteria have multi-layered cell walls, which do not retain the purple dye. The walls of these bacteria instead show the red dye that is used as a background stain.