Health Library

Our Health Library information does not replace the advice of a doctor. Please be advised that this information is made available to assist our patients to learn more about their health. Our providers may not see and/or treat all topics found herein.

Gram stain

A Gram stain is a type of test that helps tell whether bacteria causing an infection are Gram-positive or Gram-negative. This can help a doctor choose the best treatment for an infection.

The Gram stain is done by putting a special dye on the bacterial cells. Gram-positive bacteria retain the dye and turn a different color than Gram-negative bacteria do. Sometimes more testing is done after the Gram stain to identify the specific kind of bacteria and the antibiotics that can kill them.