Gram Positive vs Gram Negative Bacteria

It was in 1884 when Hans Christian Gram, a Danish bacteriologist, devised a test and introduced a dye to the bacteria to check if bacteria had a peptidoglycan wall or simply a mesh-like layer of amino acids and sugars. The same method of "Gram staining" is still in use to distinguish between gram positive and gram negativebacteria. Let's find more about it.

Difference in Gram Positive vs. Gram Negative Reaction

Different types of bacteria have been identified already, but they are classified differently. One way to classify them is to perform Gram staining test to check if they belong to gram positive category or are gram negative bacteria.

During a Gram stain test, bacteria are dyed crystal violet and then are washed with a decolorizing solution. After washing, a counterstain is added, which is usually fuchsine or safranin. This changes Gram-negative bacteria to pink or red, while Gram-positive bacteria maintain their violet dye.

This mainly happens because their difference in the structure of cell walls: there is no outer cell membrane in Gram-negative bacteria; however, the cell wall of Gram-positive bacteria is different and is high in peptidoglycan.

Other Differences Between the Two Types of Bacteria

In the war of gram positive vs. gram negative bacterial, there are some obvious differences. Here is more about it.


Gram Positive Bacteria

Gram Negative Bacteria

Peptidoglycan layer

Thick, multilayered

Thin, single-layered

Teichoic acids

Present in many


Periplasmic space



Lipopolysaccharide (LPS) content

Virtually none


Outer membrane



Flagellar structure

2 rings in basal body

4 rings

Lipid and lipoprotein content



Toxins producuts

Primarily exotoxins

Primarily endotoxins

Resistance to physical disruption



Susceptibility to anionic detergents



Inhibition by basic dyes



The intensity of resisting sodium azide



The intensity of resistance to drying



Cell wall composition

The thickness of cell wall is 20-30 nm, and it is smooth. The wall has 70-80% murein with low lipid content. It also contains teichoic acid.

The thickness of cell wall is 8-12 nm. It is wavy and contains 10-20% murein. It comes in contact with plasma membrane at a few loci. It does not contain techoic acid but lipid content is between 20 and 30%.

Gram Positive vs. Gram Negative: Which Is Worse?

Making a comparison of gram-positive and gram-negative bacteria helps find information about how these bacteria behave. Their structure tells a lot about how hard it is to kill them. Gram-negative bacteria are usually much harder to kill, and here comes more.

The wall of gram positive bacteria is like a heavy, thick wooden fence, whereas the wall of gram-negative bacteria is more like a thin bulletproof Kevlar vest. What it implies is that gram positive bacteria have a thick outer covering, which can absorb foreign material with ease. The membrane of gram-negative bacteria is not thick, but it is still nearly impossible to penetrate.

All in all, gram-positive bacteria have a cell membrane about 20-fold thicker as compared to the protective membrane of gram-negative bacteria. It is due to this particular reason that gram-negative bacteria are a lot more resistant to antibiotics as compared to other types of bacteria with thicker walls.

A List of Gram Positive and Gram Negative Bacteria

When comparing gram positive vs. gram negative bacteria, you can find a long list of both types of them. They are responsible for causing different types of infections and ailments. The following chart will provide you with some information about both gram-positive and gram-negative bacteria.

Gram-Positive Bacteria


Brief Intro


They are responsible for causing cavities and filamentous respiratory diseases.


They are associated with food poisoning.


They have different strains responsible for causing food poisoning, botulism, gas, gangrene, and tetanus.


They include pleiomorphic C diphteriae.


They include vancomycin resistant E (VRE) bacteria that are quite resistant to many antibiotics.


They are associated with vaginities.


This genus of bacteria helps form vaginal flora.


These are fetal pathogens responsible for newborn meningitis.


This genus of bacteria does not have cell wall and are responsible for walking pneumonia.


They may cause tuberculosis – M leprae and M tuberculosis are in this genus of bacteria.


This strain of gram positive bacteria includes S pneumonia, s mutants, and s pyogenes.

Gram-Negative Bacteria


Brief Intro


They are short rod-like organisms and also include B pertussis, which is an aerobic, pathogenic coccobacillus of the genus Bordetella.


This small parasitic bacterium is like a virus and is responsible for causing diseases such as psittacosis, trachoma, and non-specific urethritis.


It is from the genus of faculatiely anaerobic, non-spore-forming bacteria and can cause urinary tract infections, soft-tissue infections, septic arthritis, CNS infection, osteomyelitis, and more.


This type of bacteria has rod-like shape and is responsible for peptic ulcer.


This type of bacteria has a rod-like appearance and is responsible for hemorrhagic penumonia.


It colonizes the mucosal surfaces and also includes N meningitides and N gonorrheae.


This rod-shaped bacterium is responsible for causing urinary tract infections.


It is a genus of aerobic gammaproteo bacteria and demonstrates a great deal of metabolic activity.

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