A Gram stain is a laboratory procedure used to detect the presence of microorganisms, especially bacteria, in a sample taken from the site of a suspected infection. It gives relatively quick results as to the general type of bacteria that may be present. The Gram stain involves applying a sample from the infected area onto a glass slide and allowing it to dry. The slide is then treated with a series of special stains and examined under a microscope by trained laboratory staff. It is based on the principle that most bacteria are visualised under the microscope more easily after staining, which gives them a colour, depending on the type of cell wall. Any bacteria that may be present are categorised by colour and shape during the microscopic evaluation.