What is gram stain used for?

A Gram stain is a common laboratory test that is widely used to detect the presence of bacteria at the side of a suspected infection or in certain bodily fluids. If a bacterial infection is detected, the test further indicates if the infection is Gram-positive or Gram-negative. The test works by differentiating bacteria by the physical and chemical properties of their cell walls. Gram stain may also be used to diagnose fungal infections.