Gram Stain

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Gram Stain

Este artigo foi revisto pela última vez em

10 de Junho de 2006.

Este artigo foi modificado pela última vez em

19 de Junho de 2018.

At a Glance

Why Get Tested?

To identify the presence of in a patient’s specimen so that appropriate treatment can be given

When To Get Tested?

If your doctor suspects that you have a bacterial infection

Sample Required?

or fluid taken from the site of infection

What is being tested?

A Gram stain is used to determine if are present in an area of the body that is normally sterile, such as spinal fluid. A sample from the infected area is smeared on a glass slide and allowed to dry. A series of stains and a decolorizer is applied. The stained slide is then examined under a microscope where bacteria appear either purple (gram positive) or pink (gram negative). The test is named for Dr. Christian Gram, who invented the process.

A Gram stain can predict the type of bacteria causing an infection, such as pneumococcal pneumonia or a staphylococcal abscess. Viruses cannot be seen with a Gram stain since they lack the cell wall, which takes up the stain.

How is the sample collected for testing?

Usually, samples are collected using sterile swabs to obtain cells or at the site of suspected infection. Body fluids may be collected in sterile containers or by needle and syringe.

Common Questions

How is it used?

A Gram stain and culture of the material from an infected site are the most commonly performed microbiology tests used to identify the cause of an infection. Often, determining whether an infection is caused by an organism that is Gram positive or Gram negative will be sufficient to allow a doctor to prescribe treatment with an appropriate antibiotic while waiting for more specific tests to be completed. Absence or presence of white blood cells in the Gram stain can determine the adequacy of the specimen.
When is it ordered?

A Gram stain is done with a bacterial culture when a bacterial infection is suspected.
What does the test result mean?

Determining the Gram status of an organism allows the doctor to select an appropriate antibiotic before culture results are available. Gram stains cannot confirm the organism’s identity or susceptibility to antibiotics. Only a culture of the material can supply this information.
Is there anything else I should know?

Bacterial infections should not be ignored, even if the symptoms are mild. You should consult your doctor so treatment, if necessary, can begin promptly, and the spread and severity of the disease can be limited. If left untreated, bacterial infections can migrate throughout the body and cause tissue and organ damage.
What are the treatment options for bacterial infections?

Antibiotics are the main treatment of bacterial infections.
What does the doctor look for on the slide?

In addition to color, which indicates whether the organism is Gram positive or Gram negative, the shape of the organism (such as rod-shaped) and the formation of groups of organisms are informative. For example, staphylococcus (staph) bacteria are found in grape-like clusters, while streptococcus (strep) bacteria are found in pairs or chains, like a string of pearls.
What happens if my doctor needs more information than the Gram stain provides?

The Gram stain is usually done in conjunction with a culture. This allows for more exact identification of the bacteria causing the infection and determination of the most appropriate antibiotic.
Can I perform this test at home?

No. This test is performed by trained laboratory professionals.

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