April 30, 2012


Gram staining is a method used to differentiate between cell wall

characteristics by using a safranin stain that adheres to peptidoglycan (a

sugar/amino acid polymer that forms bacterial cell walls).

Gram-positive bacteria possess a thick layer of peptidoglycan exterior to

the plasma membrane that retains the dye crystal violet. They appear to be

a dark purple or blue/black.

Gram-negative bacteria have a cell wall composed of a thin layer of

peptidoglycan and lipids that is sandwiched between two plasma

membranes. Because of this, the crystal violet washes out easily and they

become stained a light red or pink color with safranin stain.

(Source: , via fyeahchemistry)