Gram Stain

∞ generated and posted on 2015.12.29 ∞

Means of differentiating microscopically between bacteria that have thick cell walls and no outer membrane from those that have thin cell walls and an outer membrane.

Gram Stain or Gram Straining is the most common differential microbiological staining procedure and is used to differentiate so-called Gram-positive and Gram-negative bacteria, ones with thick cell walls versus thin and associated outer membrane, respectively.

Gram staining is a kind of differential staining and utilizes a primary stain (crystal violet), mordant (Gram's iodine), a decolorizing agent (alcohol or acetone alcohol), and a counterstain (safranin).

Contrast for example the acid-fast stain as well as simple staining. See also Gram positive, Gram-positive cell wall, Gram negative, and Gram-negative cell wall.

Nice, animated overview of the Gram staining procedure:

The Gram staining procedure is presented without sound except for NPR playing in the background: ☺

Does a great job of showing how readily stain will splash during rinsing, though blot rather than the suggested heat drying following staining:

There in fact are quite a number of additional YouTube videos on Gram staining.