Gram stain

A gram stain is a simple test to distinguish the type of microorganism. The organism is heat fixed and differentially stained on a microscope slide to be read under a microscope. 

Study Outline

A Gram stain is conducted on all bacteria and yeasts. A Gram stain is essential to differentiate between Gram positive and Gram negative, cocci and bacilli organisms.

Peptidoglycan is a substance found in differing amounts within bacterial cell walls. Gram postive organisms generally have larger amounts of peptidoglycan than Gram negative organisms. During the staining process, a smear is made of the organism and then stained with crystal violet which makes the cells purple. Iodine is then applied and it forms a complex with the crystal violet which is "locked" within the walls of the peptidoglycan in Gram positive organisms. A decolorizer such as acetone or methanol is applied which washes away the crystal violet/iodine complex in Gram negative organisms but not in Gram positive organisms. Last, safranin is applied as a counterstain which stains the Gram negative bacteria pink, but the Gram positive organisms remain purple.

Sample Requirements

Minimum sample size: Organism in viable media culture.
(However, there is a minimum lab charge of $75.00. )

Sample Requirements

Minimum sample size: Organism in viable media culture.
(However, there is a minimum lab charge of $75.00. )