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Gram Positive Bacteria

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  • Last Updated : 20 Oct, 2022
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Gram-positive bacteria are those that respond positively to the Gram stain test in bacteriology. This test is commonly used to swiftly divide bacteria into two categories based on the type of cell wall they have.

When viewed under an optical microscope, gram-positive bacteria look purple because they have taken up the test’s crystal violet stain. This is due to the fact that the stain is retained in the bacterial cell wall’s thick peptidoglycan layer even after it has been rinsed from the rest of the sample during the test’s decolorization phase. However, alcohol employed in this stage damages the outer membrane of gram-negative cells, making the cell wall more porous and preventing gram-negative bacteria from retaining the crystal violet stain following the decolorization step. Because of their much thinner peptidoglycan layer wedged between a bacterial outer membrane and an inner cell membrane, they pick up the counterstain (safranin or fuchsine) and become visible in red or pink color. 

Gram-positive bacteria are more susceptible to several cell wall-targeting antibiotics than gram-negative bacteria because they lack the outer membrane while having a thicker peptidoglycan layer.

Gram-Positive Bacteria



A gram-positive bacteria’s cell wall is made up of the following

  • Peptidoglycan- It is a porous, cross-linked organic polymer with a stiff structure that is crucial in giving the cell wall shape and strength. About 90% of the cell wall surrounding the plasma membrane is made up of this substance, which shields the cell from its surroundings. The Glycan backbone, Peptide, and Tetra-peptide make up the three primary parts of peptidoglycan.
  • Lipid- The gram-positive bacteria’s cell wall has a lipid component that aids in the cell wall’s attachment to the cell membrane. The overall lipid content in the cell walls of gram-positive bacteria ranges from 2 to 5%.
  • Acid teichoic- It is a glycerol polymer that is water-soluble. Teichoic acid, which accounts for about 50% of the total dry weight of the cell wall, is the main surface antigen of gram-positive bacteria.


  • They also have a cytoplasmic lipid membrane and a thick coating of peptidoglycan.
  • There is no outer membrane on these bacteria.
  • Include more teichoic acids and less fat.
  • They use motility organs like cilia and flagella to move about.
  • Teichoic acid is found in the walls of Staphylococcus aureus and Streptococcus faecalis.
  • Produce exotoxins. 
  • Stained purple by gram-staining. 


Gram-positive bacteria are further classified into the following groups based on various characteristics:

  • Gram-positive cocci- Cocci that are gram-positive have an oval or round form. The word cocci, which means sphere, suggests that germs are typically spherical. Gram-positive cocci are any of the following:
    • StaphylococcusStaphylococcus grows in clusters resembling grapes. They often live without producing issues on our skin and mucous membranes. However, staphylococci can result in life-threatening infections if they enter the body.
    • Streptococcus- Chains of streptococcus bacteria develop. This occurs as a result of incomplete cell division after division. Streptococci are typically found in the body, just like staphylococci. They are commonly found in the mouth, vaginal tract, intestinal tract, and skin.
  • Gram-positive bacilli- Bacilli is the name for gram-positive bacteria that have a rod-like form. The majority of these bacteria are normally found on the skin, but some of them can lead to life-threatening illnesses. 


Staphylococcal species are responsible for the sharp rise in skin and mucous infection rates across the board in humans. These microorganisms are primarily spread by pets, fomite contact, inhaling infected aerosolized particles, and skin contact. Other risk factors include diphtheria, mycobacterium tuberculosis, respiratory illnesses, cavities in the teeth, and food poisoning.

Gram Stains

A test called a “gram stain” looks for bacteria in suspected infection sites such as the throat, lungs, genitalia, or skin wounds. Gram stains can also be used to examine the presence of germs in bodily fluids like blood or urine.

Gram-positive and Gram-negative infections are the two primary subtypes of bacteria. Based on how the bacteria respond to the Gram stain, several types are identified. The hue of a Gram stain is purple. The bacteria in a sample will either stay purple or change to pink or red when the stain and bacteria interact. The bacteria are Gram-positive if they continue to be purple. The bacteria are Gram-negative if they turn pink or crimson. Different forms of illnesses are brought on by the two categories:

  • Methicillin-resistant Staphylococcus aureus (MRSA), strep infections, and toxic shock are all examples of gram-positive infections.
  • Salmonella, pneumonia, urinary tract infections, and gonorrhea are examples of gram-negative infections.
    Your doctor can determine the sort of illness you have and the best drugs to use to treat it by knowing whether the bacteria are Gram-positive or Gram-negative.


Gram-negative bacteria are di-derms, which have two lipid bilayers, while gram-positive bacteria are mono-derms, which have just one. Some species (including the Mollicutes class, some Rickettsiales members, and the insect-endosymbionts of the Enterobacteriales) lack peptidoglycan and are gram-variable. However, this is not always the case. Although they share a two-layer structural design with gram-negative bacteria, Deinococcota exhibit gram-positive staining. With a few exceptions, the Chloroflexota have a single layer but do not stain. The TM7 clade and the Ktedonobacteria, two phyla allied to the Chloroflexi, are likewise mono-derms.

Only a few Bacillota species are gram-negative. These are members of the classes Negativicutes, which include Selenomonas and are gram-negative, and Mollicutes, which lack peptidoglycan and are alternatively thought of as a class of the phylum Mycoplasmatota. Additionally, it has been discovered that a variety of bacterial taxa, including Negativicutes, Fusobacteriota, Synergistota, and Elusimicrobiota, that belong to the phylum Bacillota or branch out from it, have di-derm cell structures.


One of three procedures for horizontal gene transfer, the other two being conjugation (transfer of genetic material between two bacterial cells in close contact) and transduction, occurs when external genetic material moves from a donor bacterium to a receiver bacterium (injection of donor bacterial DNA by a bacteriophage virus into a recipient host bacterium). When genetic material is transformed, it travels through the intermediary medium and is entirely absorbed by the recipient bacterium.

Risk of Gram-positive Bacteria

The cocci Staphylococcus aureus is gram-positive, catalase-positive, and coagulase-positive. Skin infections, pneumonia, endocarditis, septic arthritis, osteomyelitis, and abscesses are inflammatory diseases that S. aureus can cause. Additionally, S. aureus can result in scalded skin syndrome (exfoliative toxin), toxic shock syndrome (TSST-1), and food poisoning (enterotoxin).

The gram-positive, catalase-positive, coagulase-negative, and novobiocin-sensitive Staphylococcus epidermidis form clusters and is coagulase-negative. Biofilms are frequently created when S. epidermidis infects IV catheters and prosthetic devices. Staphylococcus saprophyticus is a common flora of the vaginal tract and perineum and is novobiocin resistant. The second most frequent cause of an uncomplicated urinary tract infection is S. saprophyticus.


  • These non-pathogenic bacterial species live inside of us in places including the mouth, skin, intestine, and upper respiratory system.
  • They are a necessary component in the creation of Emmentaler or Swiss cheese.
  • The Corynebacterium species are employed in the manufacturing of enzymes, amino acids, nucleotides, etc.
  • Large amounts of enzymes are secreted using a variety of Bacillus species.
  • A few gram-positive bacterial species are also involved in the aging of cheese, bioconversion of steroids, hydrocarbon breakdown, etc.
  • The gram-positive bacterium Bacillus amyloliquefaciens is a good source of the natural antibiotic protein. Barnes. 

FAQs on Gram-positive Bacteria

Question 1: What illnesses are brought on by gram-positive bacteria?


Staphylococcus aureus is a clustering gram-positive, catalase-positive, and coagulase-positive cocci. S. Skin infections, pneumonia, endocarditis, septic arthritis, osteomyelitis, and abscesses are just a few of the inflammatory illnesses that aureus can cause.

Question 2: Name some types of gram-positive bacteria. 


Gram-positive bacteria can be staphylococci, streptococci, pneumococci, Bacillus anthracis, and Corynebacterium diphtheria.

Question 3: Where can you find gram-positive bacteria?


Gram-positive bacteria spores can be found in soil, air, and even inside human bodies.

Question 4: How are gram-positive bacteria treated? 


The majority of illnesses caused by Gram-positive bacteria can be treated with just a few medications. 90% of Gram-positive infections should be treated by penicillin, cloxacillin, and erythromycin.

Question 5: What exactly does being Gram-positive mean?


Bacteria that are gram-positive have thick cell walls. These microorganisms produce a positive Gram stain test result. The bacterium’s cell wall turns purple during the test, which uses a chemical dye. On the other hand, gram-negative bacteria don’t absorb the dye. They instead stain pink.

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