Gram stain test is a laboratory procedure that detects the presence and identify the general type of bacteria and sometimes fungi (microbes) in a sample taken from the site of a suspected infection. It generally classify bacteria grown in culture so that further identification tests can be performed and appropriate treatment to given.
A Gram stain test checks for bacteria at the site of a suspected infection or in certain body fluids, such as blood or urine. These sites include the throat, lungs, and genitals, and in skin wounds.
There are two main categories of bacterial infections: Gram-positive and Gram-negative. The categories are diagnosed based on the how the bacteria reacts to the Gram stain. A Gram stain is colored purple. When the stain combines with bacteria in a sample, the bacteria will either stay purple or turn pink or red. If the bacteria stays purple, they are Gram-positive. If the bacteria turns pink or red, they are Gram-negative.