MedlinePlus Medical Encyclopedia: Stool Gram stain

Skip navigation


Medical Encyclopedia
Other encyclopedia topics:	A-Ag Ah-Ap Aq-Az B-Bk Bl-Bz C-Cg Ch-Co Cp-Cz D-Di Dj-Dz E-Ep Eq-Ez F G H-Hf Hg-Hz I-In Io-Iz J K L-Ln Lo-Lz M-Mf Mg-Mz N O P-Pl Pm-Pz Q R S-Sh Si-Sp Sq-Sz T-Tn To-Tz U V W X Y Z 0-9

Stool Gram stain

Contents of this page:
Alternative names Definition How the test is performed How to prepare for the test How the test will feel	Why the test is performed Normal Values What abnormal results mean What the risks are Special considerations

Alternative names

Gram stain of stool; Feces Gram stain

Definition Return to top

Gram stain is a method of staining microorganisms (bacteria) using a special series of stains. In this test, a specimen of stool is stained and then examined under the microscope.

The Gram stain method can be applied to almost any clinical specimen and is one of the most commonly used techniques for the rapid diagnosis of bacterial infections.

How the test is performed Return to top

A small amount of stool is applied in a very thin layer to a microscope slide. This is called a smear. A series of stains called a Gram stain is applied to the specimen. It is first stained with crystal violet stain, then iodine, then decolorized, then stained with safranin.

The stained smear is then examined under the microscope for the presence of bacteria. The color, size, and morphologic appearance (shape) of the cells help identify the infecting organism.

How to prepare for the test Return to top

Adults and children:
There are many ways to collect the samples. You can catch the stool on plastic wrap that is loosely placed over the toilet bowl and held in place by the toilet seat. Then, put the sample in a clean container. One test kit supplies a special toilet tissue that you use to collect the sample, then put the sample in a clean container.

Infants and young children:
For children wearing diapers, line the diaper with plastic wrap. If the plastic wrap is positioned properly, isolating the stool from any urine output, mixing of urine and stool can be prevented for a better sample.

How the test will feel Return to top

Some people feel discomfort or embarrassment with this test.

Why the test is performed Return to top

The test may be performed to try to diagnose an infection or illness, sometimes involving diarrhea.

Normal Values Return to top

The presence of only normal or "friendly" organisms is normal. All humans have bacteria in their intestines.

What abnormal results mean Return to top

An intestinal infection may be present. Stool cultures and more sophisticated tests can also help diagnose the cause of the infection.

What the risks are Return to top

There are no risks.

Special considerations Return to top

Additional examinations of the specimen may be indicated for conditions other than infection.

Update Date: 1/26/2004

Updated by: Daniel Levy, M.D., Ph.D., Infectious Diseases, Greater Baltimore Medical Center, Baltimore, MD. Review provided by VeriMed Healthcare Network.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2002 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.