A gram stain is a test often used to identify the cause of a bacterial infection.
It involves taking a sample from the affected area for laboratory examination for the presence of micro-organisms.
A gram stain is sometimes carried out with a culture assessment. A culture is a population of cells, usually bacteria, grown in a liquid or solid substance.
The result of the gram stain can help determine the type of bacteria present so that treatment with an appropriate antibiotic can be started. In some cases further tests may be necessary to confirm the exact cause of the infection.