Gram-positive bacteria


Gram-positive bacteria, stained purple, of both the bacillus (“rod-shaped”) and coccus (spherical) forms. A few Gram-negative bacteria are also present, stained pink.

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 retain the crystal violet stain, instead taking up the counterstain (safranin or fuchsine) and appearing red or pink. Gram-positive organisms are able to retain the crystal violet stain because of the high amount ofpeptidoglycan in the cell wall. Gram-positive cell walls typically lack the outer membrane found in Gram-negative bacteria.