What is the Gram Stain?

Are you interested in a career in the fascinating field of microbiology? If you choose to take a microbiology lecture and lab course in college, you will likely learn how to perform a Gram stain, as well as the theory behind it.

Bacteria can react as Gram positive(+) or Gram negative(-), the reaction depends on what their cell wall is made of. Gram (+) cell walls have a thick layer of peptidoglycan, with acidic polysaccharides(multiple sugar molecules bound together). Gram(-) cell walls have a thin layer of peptidoglycan, with plenty of space between the inner and outer membrane. The outer membrane is made of lipopolysaccharides(fat and sugar molecules bound together).

To perform the Gram stain, you would place your bacteria on a slide, and apply a series of chemicals: crystal violet, iodine, ethanol, and safranin. Crystal violet gives a purple color, iodine helps bind the crystal violet within the cell wall. Ethanol decolorizes, or takes out the crystal violet and iodine. Safranin gives a pink color. Because thicker cell walls can hold the crystal violet and iodine, Gram (+) cells will appear purple, even after you add the safranin. The thinner cell walls will be easily decolorized, so they will appear pink.

This technique is especially useful to learn if you plan on working in a medical diagnostics lab. You would use the Gram stain technique on samples collected from patients, such as a tissue or urine sample. The result of the stain, (+) or (-) would give more information on the patient's condition. Some Gram (+) bacteria can cause food poisoning, endocarditis(infection near the heart), skin infections, and strep throat, among others. Gram (-) bacteria can cause pneumonia, infections in wounds/bloodstream, and meningitis, and other conditions.

While the Gram stain takes some practice, it is a valuable, widely used microbiology technique, definitely worth learning.

Picture Source: orbitbiotech.com