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 special stain and examined under a microscope by a trained laboratorian. Any bacteria that may be present are categorized by color and shape during the microscopic evaluation:
- Color — typically bacteria may be either “Gram positive” (purple) or “Gram negative” (pink)
- Shape — the most common shapes include round (cocci) or rod-shaped (bacilli)
Additional information may be obtained by observing the groupings of the bacteria on the slide, such as cocci that are present singly, in pairs, in groups of four, in clusters or in chains, or bacilli that are thick, thin, short, long, or have enlarged spores on one end. Any bacteria that are present within white blood cells (intracellular) are also noted.