Difference between Gram-Positive and Gram-Negative bacteria

A bacteria is a large group of minute, unicellular, and microscopic organisms. These are further classified as prokaryotic cells because they are lacking the true nucleus. These types of microscopic organisms comprise of a simple physical structure. Their structure includes the cell wall, capsule, DNA, pili, flagellum, cytoplasm, and ribosomes. Bacteria can be classified as gram-positive or gram-negative. This classification depends upon the staining methods. The Danish bacteriologist J.M.C. Gram has devised a method of staining bacteria. He used a dye called crystal or gentian violet. His method helps to distinguish between different types of bacteria. The gram-staining characteristics of bacteria are identified as positive or negative. And it depends upon whether the bacteria take up and retain the crystal violet stain or not. Let us have a detailed look at these two. Also, difference between gram positive and gram negative bacteria will be well presented here.

What are gram-positive bacteria?

Gram-positive bacteria retain the color of the crystal violet stain in the Gram stain. Such bacteria include staphylococci, streptococci, pneumococci. Also, some others are the bacterium which causes diphtheria and anthrax. Gram-positive bacteria show the visible violet color upon the application of mordant means iodine and ethanol. Gram-positive bacteria constitute a cell wall consisting of multiple layers of peptidoglycan. It forms a rigid and thick structure. Its cell walls additionally having teichoic acids and phosphate. The teichoic acids are of two types, one is lipoteichoic acid and the other is the teichoic wall acid.

What are gram-negative bacteria?

Gram-negative bacteria do not retain the crystal violet stain and further, it takes the color of the red counterstain in Gram’s method of staining. This is the major characteristic of bacteria that have a cell wall composed of a thin layer of peptidoglycan. Mostly these bacteria include most of the bacteria normally found in the gastrointestinal tract. Some are gonococci causing venereal disease and meningococci causing bacterial meningitis.

The gram-negative bacteria are stained by a counterstain such as safranin, also these are de-stained with the alcohol wash. Therefore, under a microscope, these are noticeably pink in color.

In gram-negative bacteria, the cell wall is consisting of an outer membrane and several layers of peptidoglycan. Whereas the outer membrane is composed of lipoproteins and phospholipids. The peptidoglycan stays intact to the lipoproteins of the outer membrane. It is located in the fluid-like periplasm between the plasma membrane and the outer membrane. The periplasm is contained with proteins and degrading the enzymes. Due to the presence of porins, the outer membrane is permeable to nutrition, water, food, iron, etc.

Difference between gram-positive and gram-negative bacteria:

The important difference between gram-positive and gram-negative bacteria in tabular form.

Parameter	Gram-positive bacteria	Gram-negative bacteria
Cell Wall	A single-layered, smooth cell wall	A double-layered, wavy cell-wall
Cell Wall thickness	The thickness of the cell wall is 20 to 80 nanometres	The thickness of the cell wall is 8 to 10 nanometres
Peptidoglycan Layer	It is a thick layer/ also can be multi-layered.	It is a thin layer/ often single-layered.
Teichoic acids	Teichoic acids are present.	Teichoic acids are not present.
Lipopolysaccharide	Lipopolysaccharide is not present.	Lipopolysaccharide is present.
Outer membrane	The outer membrane is not present.	The outer membrane is mostly present.
Lipid content	The Lipid content is very low.	The Lipid content is 20% to 30%.
Resistance to Antibiotic	These are very susceptible to antibiotics.	These are very resistant to antibiotics.

Some key points about Gram-Positive and Gram-Negative Bacteria:

Besides the above-mentioned difference between gram-positive and gram-negative bacteria, let us have some key points.

• The cell wall of gram-positive bacteria is consisting of thick layers of peptidoglycan. Whereas the cell wall of gram-negative bacteria is consisting of thin layers of peptidoglycan.
• During the gram staining procedure, a gram-positive cell retains the purple-colored stain. But do not retain the purple colored stain.
• Gram-positive bacteria produce exotoxins, whereas gram-negative bacteria produce endotoxins.
• Gram-negative bacteria cause many infections in humans. Some common illness is indigestion, food poisoning, pneumonia, meningitis, etc. Some other infections also happen in the blood cells, bloodstream, wound infections, etc. due to these bacteria.

FAQs on Gram-Positive and Gram-Negative Bacteria:

Q.1: Give some examples of gram-positive bacteria.

Answer: Some examples are Staphylococcus, Streptococcus, Enterococcus, etc.

Q.2: Which one is more harmful between gram-positive or gram-negative bacteria?

Answer: Gram-negative bacteria are considered more harmful. These cause certain diseases. Also, their outer membranes are hidden by a slime layer and it hides the antigens present in the cell.

Q.3: What infections are possible by gram-positive bacteria?

Answer: Gram-positive bacteria are generally responsible for problems like Urinary Tract Infections. These are happening in people who are more prone to such infections as old aged people and pregnant women.