Gram Staining Experiment Inventory
Materials 2 “Gram” Slides from Experiment 1
Crystal Violet
Deionized Water
Gram Iodine
Decolorizer
Safranin
*Sink or Disposable Plastic Container
*10% Bleach Solution
Labware 1/2 Bibulous Paper Sheet
Parafilm®
1 Pair of Disposable Gloves
*Lab Notebook (optional)
*Scissors
Note: You must provide the materials listed in *red.
EXPERIMENT 3: GRAM STAINING
The Gram staining technique was invented by Dr. Hans Christian Gram (1853 – 1938), a scientist who worked in microbiology labs with Robert Koch. Gram staining was a major breakthrough in the identification and classification of bacteria; it distinguishes microbes broadly into Gram-positive and Gram-negative groups. These two groups can cause very different and important health consequences. Gram-positive bacteria have thick cell walls made up of many (up to 40) layers of peptidoglycan. This thick cell wall prevents microbes from losing the purple stain (upon destaining). Gram-negative bacteria have relatively thin cell walls with only a few layers of peptidoglycan and an outer cell membrane. Gram-negative bacteria are visualized with a counterstain that creates a reddish-pink color on the bacteria.