Gram stain: what it is, purpose, procedure and results (2023)

Overview

What is a Gram stain?

A Gram stain is a laboratory test that looks for bacteria at the site of a suspected infection or in certain body fluids. A medical laboratory scientist processes the Gram stain, which provides relatively quick results, allowing health care providers to know if bacteria are present, and if so, the general types. This can help guide further identification testing and treatment options.

Bacteria are a large group of protozoa. They can live in different places on your body and on your skin. While some types of bacteria are harmless or even beneficial, others can cause infection and disease. A Gram stain helps diagnose harmful bacteria.

Under a Gram stain, different types of bacteria change one of two color groups (pink to red or purple to blue) under a special set of stains and are classified as "gram negative" or "gram positive" as appropriate. Gram stain works by distinguishing bacteria based on the chemical and physical properties of their cell walls.

However, not all types of bacteria can be tested with the Gram stain method, and Gram stains alone are usually not diagnostic. Instead, they help determine the type of bacteria in general terms.

The Gram stain is an important staining technique in microbiology that has been used by scientists for hundreds of years. It is named after the Danish bacteriologist Hans Christian Gram, who first introduced it in 1882, primarily to identify pneumonia-causing organisms.

What are gram positive and gram negative bacteria?

When bacteria are present on a Gram-stained slide, a medical laboratory scientist classifies them as Gram-negative or Gram-positive based on the color they acquire from a variety of stains. There are also gram-variable bacteria, which means they are irregularly colored, and there is a mix of pink and purple bacteria.

It is important to note that gram negative does not mean that no bacteria are present, and 'positive' and 'negative' do not mean 'good' and 'bad' in this case.

gram positive organism

Gram-positive bacteria have cell walls that contain thick layers of peptidoglycan, a substance that forms the cell walls of many bacteria. Peptidoglycan makes up about 90% of the cell wall of Gram-positive bacteria. As a result, they appear blue to violet under a Gram stain.

Gram-positive organisms include:

• staphSpecies.
• streptococciSpecies.
• CorynebacteriumSpecies.
• ClostridiumSpecies.
• ListeriaSpecies.

Gram-negative organism

Gram-negative bacteria have cell walls with thin layers of peptidoglycan (10% of the cell wall) and high levels of lipids (fatty acids). As a result, they appear red to pink under a Gram stain.

Gram-negative organisms include:

• Neisseria gonorrhoeae and Neisseria meningitis.
• MoraxellaSpecies.
• Escherichia coli(E. coli).
• PseudomonasSpecies.
• protectionSpecies.
• KlebsiellaSpecies.

What is the difference between a Gram stain and a bacterial culture?

Health care providers use a Gram stain and bacterial cultures if they suspect you have a bacterial infection. However, these tests provide different information.

Providers often order bacterial culture tests in addition to Gram stain tests. In a bacterial culture test, a medical laboratory scientist removes cells from the sample that will also be used for the Gram stain and places them in a special environment to encourage cell growth. Results are usually available in a few days, but some types of bacteria grow slowly, which can take several days or longer. Once the cells have multiplied and grown sufficiently, a medical laboratory scientist examines the cultured bacteria to determine their precise identity.

In a Gram stain, a sample is stained on glass slides and viewed under a microscope to determine if any bacteria are present. If bacteria are present, medical laboratory scientists can see if they are gram-negative or gram-positive based on whether the bacteria appear pink to red or purple to blue under the stain. The different types of bacteria are either gram negative or gram positive.

Although Gram stains provide faster results than bacterial cultures, in most cases, unlike a bacterial culture, a Gram stain cannot diagnose the type of bacteria. However, Gram stains can help point healthcare providers in the right direction for prescribing treatments.

What conditions do Gram stains help diagnose?

Health care providers order Gram stains to diagnose and treat certain bacterial infections, such as:Urinary tract infections (UTIs)and bacteriallung infection. Providers may not always order a Gram stain to help diagnose conditions caused by bacteria. For example, they do not usually change color due to food poisoning, but it is possible to do so through a stool sample (poop).

Common gram-negative bacteria and associated diseases

Examples of gram-negative bacteria (in italics) and the conditions they can cause include:

• Escherichia coli: urinary tract infections (UTIs) andpoisoned food.
• Legionella pneumoniae:legionelosis.
• salmonella: food poisoning andtyphoid fever.
• Klebsiella: Pneumonia, bloodstream infections, wound or wound infections andmeningitis bacterial.
• Neisseria gonorrhoeae:hiker.
• protection: HWI.
• morganella morganii: HWI,Septicemia, pneumonia, wound infections, musculoskeletal infections, central nervous system infections andpericarditis.
• Aeromonas: eye infections,Osteomyelitis, bacterial meningitis, respiratory infections after "near drowning" and joint infections.

Common gram-positive bacteria and their comorbidities

Examples of Gram-positive bacteria (in italics) and the conditions they can cause include:

• steotococos neumonia: Neumonia bacterial.
• staphylococcus aureus: Neumonia bacterial,Methicillin-resistant Staphylococcus aureus (MRSA)ytoxic shock syndrome.
• group A strepspecies:sore throatinfections
• Listeria: poisoned food.
• Clostridium: poisoned food
• Clostridium botulinumyClostridium butyricum:botulism.

When is a Gram test done?

Health care providers usually order a Gram stain along with a bacterial culture if they suspect you have a bacterial or sometimes fungal infection. It is one of the most common ways to quickly diagnose a bacterial infection in your body.

Who performs a Gram stain test?

Depending on the type of infection you have, many types of healthcare providers can collect a sample for a Gram stain test. For example, a gynecologist may take a swab for a Gram stain test for gonorrhea, and a pulmonologist may take a sample of your saliva or mucus to use in a Gram stain test for bacterial pneumonia.

Your provider then places the sample in a sterile container and sends it to a lab for testing. A medical laboratory scientist applies the sample to slides, applies a series of stains, and views the sample under a microscope. You compile a report and share it with your healthcare provider.

test details

How do I prepare for a Gram stain test?

You don't have to do anything special to prepare for a Gram stain test.

How is a gram stain test done?

A Gram stain test involves three general steps, including:

• collecting the sample.
• sample processing.
• sample examination.

Collect Gram stain sample

For a Gram stain test, your doctor takes a sample from a suspected site of infection. Some of the ways a provider may collect Gram stain test samples are:

• Brushing or scraping of tissue from the surface of a part of the body.
• Collection of samples of fluids or waste from your body.
• Use a fine needle aspiration to collect a sample of fluid from an area of ​​your body.

Stains picked up by a swab with brushes and scrapes include yours:

• Throat.
• nostrils
• Genitals.
• skin wounds

Samples that you can collect directly into a sterile container include:

• spit (sputum).
• Urine (Cheeks).
• Stool (poop).

Areas of your body that may require the use of fine needle aspiration include:

• synovial fluid in your joints.
• Fluid around your heart (pericardial fluid).
• Fluid around the lungs (pleural fluid).
• Cerebrospinal fluid (CSF) around the spinal cord.

Your provider then places the sample in a sterile container and sends it to a lab for testing.

Gram stain procedure

In the laboratory, a medical laboratory scientist smears or spreads the sample on glass slides. These slides are called swabs. They then apply a series of stains to the swab to perform a Gram stain.

The Gram staining process involves four basic steps, including:

1. Application of a primary colorant (crystal violet).
2. Addition of a mordant (Grams of Iodine).
3. Quick bleaching with ethanol, acetone or a mixture of both.
4. Contrast with safranin.

Gram stain test

The medical laboratory technician then classifies any bacteria that may be present by color and shape during microscopic evaluation:

• color: Typically, Gram-positive bacteria appear purple to blue, and Gram-negative bacteria appear pink to red.
• Form: The most common shapes include round (Cocina) or rod-shaped (bazillen).

The medical laboratory worker also looks for additional characteristics of the sample by looking at the clumps of bacteria on the slide. Examples include:

• CocinaThey occur singly, in pairs, in groups of four, in clusters, or in chains.
• bazillenwhich are thick, thin, short, long, or have enlarged spores at one end.
• When bacteria are present in white blood cells.

The medical lab technician then creates a report and sends it to your doctor.

What are the risks of a Gram stain test?

There is no risk of having a Gram's spot involving a swab or fluid collection of sputum (spit), urine, or feces.

There is a very small risk in blood tests. You may have a slight sensitivity or abruiseat the blood draw site, but this usually resolves quickly.

Possible risks of fine needle aspiration include:

• discomfort or pain.
• bleeding.
• Infection.
• Damage to neighboring buildings.

results and monitoring

What do the results of a Gram stain mean?

Gram stain test results show one of two categories: a negative Gram stain or a positive Gram stain. This is not to be confused with gram negative bacteria or gram positive bacteria.

Gram stain negative

If your test result shows a negative Gram stain or "no organisms seen," it usually means there are too few bacteria to see with the Gram stain method. Bacteria can still be detected by culture if the sample is cultured.

Gram stain positive

If your test result shows a positive Gram stain, it means that bacteria were present in your sample. If your result is positive, it will usually include information about what type of organism was present on the sample slide, including:

• type of bacteria: Gram-positive or gram-negative.
• form of bacteria: Around (Cocina) or smallpox (bazillen).
• Other bacterial properties: Possibly size, relative quantity (number) and/or disposition of the bacteria.
• other cells: If there are bacteria present in other cells (intracellular) and if there are red or white blood cells.
• Mushrooms: Gram stains can check for the presence of fungi in the form of yeast or mold. You may need to do further testing to identify the specific type.

This information, along with signs and symptoms and other clinical findings, will help your healthcare provider determine which treatment might be most effective, sometimes before bacterial culture results are available.

When should I know the results of the test?

Gram stains generally give quick results. However, Gram stain results are generally considered preliminary, which means that they cannot always provide a diagnosis on their own. Results of a bacterial culture and/or other tests, e.g. B. Antigen and antibody tests for certain types of bacteria may be needed to confirm a diagnosis.

When do I have to call my doctor?

If you have been diagnosed with an infection and are having problems with your treatment or your infection is not improving, contact your doctor.

A note from the Cleveland Clinic

Gram stains are a very common and often painless method of detecting the presence of a bacterial or fungal infection. While waiting for the results of a diagnostic test can be stressful, know that your medical team will support you no matter what the results. Don't be afraid to ask your doctor questions about your test or its results.