Difference Between Gram-Positive and Gram-Negative Bacteria

Gram-positive and gram-negative bacteria are two major groups of bacteria differentiated on the basis of their structure of the cell wall, and their response to a staining method called the gram stain. The main difference between Gram-positive and negative bacteria is the cell walls because of their structure and composition. Gram-positive bacteria have a thick peptidoglycan layer in their cell walls, which retains the crystal violet stain used during the staining process. While gram-negative bacteria have a thinner layer of peptidoglycan in their cell walls, which does not retain the crystal violet stain.

Gram Staining

Gram stain was developed by J.M.C. Gram, a bacteriologist from Denmark. This method uses a dye called crystal or gentian violet to differentiate between various types of bacteria. The ability of bacteria to retain the crystal violet stain determines their classification as either gram-positive or gram-negative. This staining technique is essential in identifying and characterizing different types of bacteria.

Difference Between Gram-Positive and Gram-Negative Bacteria

Features	Gram-Positive Bacteria	Gram-Negative Bacteria
Cell wall	Have a thick peptidoglycan layer in the cell wall that stains purple with Gram stain.  The cell wall is single-layered and smooth.	Have a thin peptidoglycan layer in the cell wall that stains pink with Gram stain. The cell wall is double-layered and wavy.
Cell wall thickness	The cell wall is 20-80 nanometres in thickness.	The cell wall is 8-10 nanometres in thickness.
Outer membrane	Do not have an outer membrane	Have an outer membrane outside the cell wall made of lipopolysaccharides
Morphology	Spore forming rods	Non-spore-forming rods
Flagella structure	The basal body has two rings	The basal body has four rings
Susceptibility to antibiotics	Generally more susceptible to antibiotics that target the cell wall, such as penicillin	Generally less susceptible to antibiotics that target the cell wall due to the presence of the outer membrane, but can be targeted by other antibiotics such as aminoglycosides or fluoroquinolones
Toxin production	Tend to produce exotoxins (toxins secreted by the bacteria)	Tend to produce endotoxins (toxins released upon bacterial death or lysis)
Lipid content	Low	High(20-30%)
Lipopolysaccharides	Absent	Present
Mesosomes	More prominent	Less prominent
Teichoic acid	Present in the cell wall, which helps with cell wall maintenance.	Lack teichoic acid in their cell wall.
Porins	Absent	Present in the outer membrane, form channels that allow the passage of molecules such as nutrients and antibiotics.
Gram staining	Retains crystal violet stain during gram staining	Does not retain a crystal violet stain, but gets counterstained with safranin, appearing pink or red after Gram staining.
Color	Purple	Pink or red
Endotoxin	Do not have endotoxins.	Have endotoxins in their outer membrane.
Examples	Examples include Staphylococcus, Streptococcus, and Clostridium.	Examples include Escherichia coli, Salmonella, and Pseudomonas aeruginosa.

Gram-Positive Bacteria

Gram-positive bacteria, which include staphylococci, streptococci, pneumococci, and bacteria that cause diphtheria and anthrax, are distinguished by their capacity to maintain the crystal violet stain in the Gram stain. When exposed to mordants like iodine and ethanol, these bacteria turn violet. Gram-positive bacteria’s cell wall is made up of multiple layers of peptidoglycan, resulting in a thick and strong structure. They also have teichoic acids and phosphates in their cell walls, which come in two forms: lipoteichoic acid and teichoic wall acid.

Gram-Negative Bacteria

Gram-negative bacteria are distinguished by their inability to retain the crystal violet stain during the Gram-staining process. Instead, they absorb the red counterstain due to the thin coating of peptidoglycan in their cell wall. These bacteria can cause diseases such as venereal disease and bacterial meningitis and are typically found in the gastrointestinal tract.

Gram-negative bacteria are stained with a counterstain, such as safranin, and subsequently de-stained with an alcohol wash. Under a microscope, this mechanism causes the bacteria to appear pink. Gram-negative bacteria’s cell wall is made up of an outer membrane and many layers of peptidoglycan. The outer membrane is made up of lipoproteins and phospholipids and is still connected to the peptidoglycan layer. Enzymes and proteins are found in the periplasm, which is positioned between the plasma membrane and the outer membrane. Because of the presence of porins, the outer membrane is permeable to nutrients, water, and other important elements.

FAQs on Gram-Positive and Gram-Negative Bacteria

Q1: Are gram-negative or gram-positive bacteria more harmful?

Answer:

Gram-negative bacteria are more harmful than gram-positive because they have hard protective outer shells which help negative bacteria to resist antibiotics.

Q2: Is E-coli a gram-negative or gram-positive bacteria?

Answer:

E.coli is a gram-negative bacteria.

Q3: What infection is caused by Gram-positive bacteria?

Answer:

Gram-positive bacteria can cause various infections, with urinary Tract Infections being a common example, particularly in vulnerable populations such as the elderly and pregnant women.

Q4: Which infections are caused by gram-negative bacteria?

Answer:

Gram-negative bacteria cause various infections in humans:

• Indigestion
• Food Poisoning
• Pneumonia