Everything You Need To Know About Gram-Negative Bacteria

This article will be looking into Gram-negative bacteria, what they are, and how you can identify them.

Everything You Need To Know About Gram-Negative Bacteria

We will explain what Gram-negative bacteria are and how they differ from Gram-positive bacteria, and how you can discover them through the Gram staining process.

What Is Gram Staining?

Gram staining was first developed in the year 1884 and was named for its inventor: Danish bacteriologist Hans Christian Gram.

When Gram staining is used, it won’t be able to define the exact bacteria species, but it helps narrow the possibilities by identifying whether it is Gram-positive or Gram-negative.

Gram staining is used to differentiate two distinct groups of bacteria, such as Gram-positive and Gram-negative. These are distinguished by coloring the cells that are stained either red or violet.

While Gram-positive bacteria will appear violet due to a thick layer of peptidoglycan in the cell walls, Gram-negative bacteria will stain red due to their thinner peptidoglycan walls. 

There are three processes involved with Gram staining. They have a water-soluble dye known as crystal violet, which they dye the cells with.

They use a decolorizer, either acetone or ethyl alcohol, to dehydrate the peptidoglycan layer.

Then, they counter-stain it with a weakly water-soluble safranin which is lighter than crystal violet, so it doesn’t disrupt the purple coloration of any Gram-positive bacteria. However, decolorized Gram-negative cells will turn red.

Distinction Of Gram-Negative Bacteria After Gram Staining

As mentioned above, Gram-negative bacteria will have a pale red color after the cell has been through the Gram staining process.

This is due to the thin peptidoglycan layer on the cell wall, as it cannot retain the crystal violet dye. Instead, it is colored by the counterstain.

Under a microscope, you will notice that the outer lipid membrane is present, as are O-specific side chains. However, you won’t find any Teichoic and lipoteichoic acids. 

Examples Of Gram-Negative Bacteria

There are numerous examples of Gram-negative bacteria, with a list formed below of the numerous species that have been accounted for when used in the Gram staining process.

  • Salmonella
  • Shigella
  • Enterobacteria
  • Pseudomonas
  • Hilecobacter
  • Stenotrophomonas
  • Bdellovibrio
  • Legionella
  • Cyanobacteria
  • E. coli
  • Klebsiella
  • Proteus
  • Providencia
  • Morganella
  • Aeromonas
  • Citrobacter

Many of the associated bacteria on this list include species that have various members, and this is not a definitive list. However, if you look for any members of these groups, you will find that they all share their Gram-negative status.

The most common causes of Gram-negative infections are E. coli, Salmonella, Pseudomonas aeruginosa, and Klebsiella.

Many of these Gram-negative bacteria have been discovered to have outbreaks in hospitalized settings and have case studies that have allowed a better understanding of how healthcare professionals can prevent outbreaks. 

What Does It Mean To Be Infected With Gram-Negative Bacteria?

Gram-negative bacteria can cause major infections and are especially dangerous when they occur in healthcare settings.

If someone is infected with Gram-negative bacteria, they could suffer from bloodstream infections, meningitis, and pneumonia.

Unfortunately, Gram-negative bacteria are increasingly resistant to antibiotics, and so they are a significant risk to immunocompromised patients when outbreaks occur.

Gram-negative bacteria can easily pass into the body through penetrative medical devices such as IVs or catheters.

You could also catch them if you come into contact with someone carrying Gram-negative bacteria, especially if they have an open wound.

To avoid this, it is essential that good hygiene is maintained in healthcare settings and that any penetrative medical devices are not recycled to be used on other patients.

It is also why wounds should always be cleaned and bandaged, as Gram-negative bacteria can have a significant impact on your health.

How Do You Treat An Infection Caused By Gram-Negative Bacteria?

Due to the high resistance to antibiotics that Gram-negative bacteria have, you may find that most common antibiotics won’t work.

However, your doctor may try different antibiotics to help treat the infection and ensure you no longer have it. 

When treating Gram-negative bacteria, it is better to treat prevention as the cure.

By preventing the possibility of a Gram-negative bacteria outbreak through good hygiene practices and controlling infections, the chance of Gram-negative bacteria spreading can become thinner. 

It is also an excellent idea to understand where bacteria can be found, even in nature. If you accidentally ingest Gram-negative bacteria through water sources, it is vital that you get immediate medical treatment.

This is why, when traveling, you should ensure that you keep an eye on water quality and never drink water in another country unless you know that it has been filtered and is safe to drink.

The same can also be said when you go swimming.

How Do You Diagnose A Gram-Negative Infection?

Your symptoms will vary when you have a Gram-negative infection, but you may notice that fever will be a common sign.

Your doctor is likely to inquire about any of your symptoms and your health history, and if you have been traveling. 

Gram staining is only one process used when identifying a specific Gram-negative bacteria, as all have different treatment methods.

You will have blood tests and urine tests conducted, and you may also have other more significant tests depending on the severity of your infection. 

Depending on where your infection is, they will test for any bacteria where they suspect the infection to be, but primarily, they will take blood or urine samples for the Gram staining process. 


Gram-negative bacteria appear on Gram stain tests with a reddish color due to the counterstaining process and their inability to retain violet dye.

They are resistant to antibiotics and can be dangerous in hospital settings. If you ingest any Gram-negative bacteria, they can cause significant medical risks, including pneumonia and meningitis. 

The best way to handle any infections from Gram-negative bacteria is to ensure that preventative measures are taken.

If you don’t follow standard hygiene procedures, there is a high possibility that Gram-negative bacteria could cause an outbreak.

Prevention is the best way of treating Gram-negative bacteria due to their significant resistance to antibiotic treatments.

Jennifer Dawkins

Leave a Comment

Your email address will not be published. Required fields are marked *