Gram-positive

Gram-positive bacteria retain the color of the crystal violet stain in the Gram stain.

This is characteristic of bacteria that have a cell wall composed of a thick layer of a particular substance (called peptidologlycan).</P> The Gram-positive bacteria include staphylococci ('staph'), streptococci ('strep'), pneumococci, and the bacterium responsible for diphtheria (Cornynebacterium diphtheriae) and anthrax (Bacillus anthracis).</P> The Danish bacteriologist J.M.C.

Gram (1853-1938) devised a method of staining bacteria using a dye called crystal (gentian) violet.

Gram's method helps distinguish between different types of bacteria.

The gram-staining characteristics of bacteria are denoted as positive or negative, depending upon whether the bacteria take up and retain the crystal violet stain or not.