Gram staining (or Gram's method) is a method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative).
It is based on the chemical and physical properties of their cell walls. Primarily, it detects peptidoglycan, which is present in a thick layer in Gram positive bacteria. A Gram positive results in a purple/blue color while a Gram negative results in a pink/red color.
The Gram stain is almost always the first step in the identification of a bacterial organism, and is the default stain performed by laboratories over a sample when no specific culture is referred.
While Gram staining is a valuable diagnostic tool in both clinical and research settings, not all bacteria can be definitively classified by this technique, thus forming Gram-variable and Gram-indeterminate groups as well.
Other articles related to "gram staining, gram":
... Gram staining is used to determine gram status to classify bacteria broadly ... Gram staining uses crystal violet to stain cell walls, iodine as a mordant, and a fuchsin or safranin counterstain to mark all bacteria ... Gram status is important in medicine the presence or absence of a cell wall changes the bacterium's susceptibility to some antibiotics ...
... Gram-indeterminate bacteria do not respond to Gram staining and, therefore, cannot be determined as either Gram-positive or Gram-negative ... Examples of them, but not limited to, are Gram-variable and acid fast bacteria ...