Primus Pathology Laboratory

Gram Stain

Last Updated on July 25, 2022 by Dr. Neeraj Gujar

What is Gram Stain Test?

Gram stain is a test to check for bacteria in the area of suspected infections such as the throat or genitals. Gram stain can also be used for checking for bacteria in blood and urine.

There are two major categories of bacterial infection: Gram-positive and Gram-negative. These categories are determined by how bacteria react to the Gram stain. A Gram stain is purple. The stain reacts with bacteria to form a color. It can stay purple, pink, or red depending on whether the bacteria are present in the sample. Gram-positive bacteria are those that remain purple. Gram-negative bacteria are those that turn pink or red. These two types of bacteria can cause different types and kinds of infections.

  • Gram-positive infections include strep infections, methicillin-resistant Staphylococcus aureus (MRSA), and toxic shock.
  • Gram-negative infections can include pneumonia, salmonella, UTI (Urinary tract infections), and gonorrhea.

Your health provider can identify whether your bacteria are Gram-positive or Gram-negative and prescribe the best antibiotics to treat them.

Your doctor may order a culture or gram stain to confirm that you have an infection. This test can help determine if there are any bacteria present. Their recommended treatment plan may be affected by the difference between gram-negative and gram-positive bacteria.

Gram staining can be done on a variety of specimens including:

  • Blood
  • Urine
  • Tissue
  • Stool
  • Sputum

Also Read: How Do Doctors Use Renal Function Test to Diagnose Kidney Diseases

Why Test Is Done?

A Gram stain is used most commonly to determine if you have an infection. A Gram stain will tell you if your infection has gone to the Gram-positive or Gram-negative side.

To diagnose fungal infections, a Gram stain can also be used.

If you are experiencing symptoms of infection, your doctor may order a Gram stain. The doctor may not be able to determine if the infection has been caused by bacteria, viruses, fungi, parasites, or both. Different types of infections can be treated differently. Different types of bacterial infections may require different treatments.

A gram stain can be used by your doctor to determine if bacteria is responsible for your symptoms. Your doctor may order additional tests to diagnose your illness.

woman sneezing spreading germs

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When To Get Tested?

If you are suffering from symptoms of a bacterial illness, this test may be necessary. Pain and fever are all common symptoms of many bacterial infections. Fatigue is another. The type of infection and the location will determine the symptoms you experience.

How To Get Tested?

Your doctor will need to take a sample of your body fluid or tissue to conduct a gram test. The type of sample they require will determine the collection method used by doctors. They may ask for sputum samples, and you might be asked to give them. They may ask for a sample of urine. They may also perform a blood draw to collect a sample.

Once they have taken the sample, they will send it to a laboratory for analysis. To make it easier to spot bacteria under a microscope, a technician will use special staining techniques.

Before the Test

You don’t need any special preparations for a Gram stain.

During the Test

Your doctor will need to collect a sample of the suspected infection site or certain bodily fluids. This depends on the type of infection.

After The Test

A blood test is not a risky procedure. Although you may feel a little bit of pain or bruise around the site where the needle was inserted, most symptoms disappear quickly.

Other sample tests are not reported with any side effects either.

Test Results

The Gram stain will be applied to the sample and placed on a slide. The slide will be examined by a laboratory professional under a microscope. If there are no bacteria found on the slide, this means that you don’t have any bacterial infection.

You might find bacteria in your body. These characteristics could be useful for diagnosing your infection.

  • If the bacteria are colored purple, it indicates that you have a Gram-positive disease.
  • You likely have a Gram-negative infection if the bacteria are colored pink or red.

The results will include information about the form of the bacteria found in your sample. Most bacteria can be either round (known by cocci) or oval (known as bacilli). You can find out more about your infection by looking at the shape of the bacteria.

Your results  for the Gram stain test might not be able to identify exactly what bacteria was in your sample. However, they will help your provider determine the cause of your illness and recommend how to treat it. To confirm the type of bacteria, you may need to run additional tests such as a bacteria culture.

Also Read: Top 9 Annual Blood Tests to Keep You Healthy and Active

You may also find a fungal infection by analyzing your Gram stain test results. These results could indicate whether you have yeast or mold fungal infections. However, you might need to run additional tests to determine the specific fungal infection.

Talk to your doctor if you have any questions about your results.


What are the 2 types of Gram stain?

Gram staining is a bacteriological laboratory technique that differentiates bacterial species into two large groups i.e., gram-positive and gram-negative depending on the physical properties of their cell walls.

What are the differences between Gram-positive and gram-negative cells?

Gram-negative bacteria are surrounded by a thin cell wall and an outer membrane. Whereas Gram-positive bacteria lack an outer membrane.

Which antibiotics treat gram-positive bacteria?

Most of the infections are seen because of Gram-positive bacteria. This is mostly treated with antibiotics like cloxacillin, penicillin, and erythromycin.

by Dr. Neeraj Gujar

Dr. Neeraj Gujar has done his M.D. in Pathology from Government Medical College. He has worked at various organisations such as Breach Candy Hospital and Tata Memorial Hospital along with many other private organisations. During his working career, he realised the pressing need for exceptional quality diagnostic services. A diagnostic centre that can consistently give accurate results verified by a consultant doctor (M.D. Pathologist) on which your doctor can depend. This has been the founding principle of Primus Pathology and Diagnostics.

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