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Gram-positive bacteria
Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
 are those that are stained dark blue or violet by Gram staining
Gram staining

Gram staining is an empiricism method of differentiating bacterium species into two large groups based on the chemical and physical properties of their cell walls....
. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain
Counterstain

A counterstain is a staining with color contrasting to the principal stain, making the stained structure more easily visible.An example is the malachite green counterstain to the fuchsine stain in the Gimenez stain....
 (safranin
Safranin

Safranin is a staining used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring all cell nucleus red....
 or fuchsin) and appearing red or pink.






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Gram Stain Anthrax
Gram-positive bacteria
Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
 are those that are stained dark blue or violet by Gram staining
Gram staining

Gram staining is an empiricism method of differentiating bacterium species into two large groups based on the chemical and physical properties of their cell walls....
. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain
Counterstain

A counterstain is a staining with color contrasting to the principal stain, making the stained structure more easily visible.An example is the malachite green counterstain to the fuchsine stain in the Gimenez stain....
 (safranin
Safranin

Safranin is a staining used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring all cell nucleus red....
 or fuchsin) and appearing red or pink. Gram-positive organisms are able to retain the crystal violet stain because of the high amount of peptidoglycan
Peptidoglycan

Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria, forming the cell wall....
 in the cell wall
Cell wall

A cell wall is a tough, flexible and sometimes fairly rigid layer that surrounds some types of cell . It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism....
. Gram-positive cell walls typically lack the outer membrane found in Gram-negative bacteria.

Characteristics

The following characteristics are generally present in a Gram-positive bacterium:
  1. cytoplasmic lipid membrane
  2. thick peptidoglycan
    Peptidoglycan

    Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria, forming the cell wall....
     layer
    • teichoic acids and lipoteichoic acid
      Lipoteichoic acid

      Lipoteichoic acid is a surface-associated adhesion amphiphile from Gram-positive bacteria. These organisms have an inner membrane and, external to it, a thick peptidoglycan layer.It contains wall teichoic acids, long chains of sugars made by ribitol or glycerol and phosphate embedded in the peptidoglycan layer....
      s are present, which serve to act as chelating
      Chelation

      Chelation is the binding or complex of a bi- or multidentate ligand. These ligands, which are often organic compounds, are called chelants, chelators, chelating agents, or sequestration....
       agents, and also for certain types of adherence.
  3. capsule polysaccharides (only in some species)
  4. flagellum
    Flagellum

    A flagellum is a tail-like structure that projects from the cell body of certain prokaryotic and eukaryotic cells, and it functions in locomotion....
     (only in some species)
    • if present, it contains two rings for support as opposed to four in Gram-negative bacteria because Gram-positive bacteria have only one membrane layer.


Classification

In the original bacterial phyla, the Gram-positive organisms made up the phylum Firmicutes
Firmicutes

The Firmicutes are a division of bacterium, most of which have Gram-positive cell wall structure. A few, the Mollicutes or mycoplasmas, lack cell walls altogether and so do not respond to Gram staining, but still lack the second membrane found in other Gram-negative forms....
, a name now used for the largest group. It includes many well-known genera such as Bacillus
Bacillus

Bacillus is a genus of rod-shaped bacterium and a member of the division Firmicutes. Bacillus species are either obligate or facultative aerobes, and test positive for the enzyme catalase....
, Listeria
Listeria

Listeria is a bacterial genus containing six species. Named after the English surgeon, Joseph Lister, Listeria species are Gram-positive bacilli and are typified by Listeria monocytogenes, the causative agent of listeriosis....
, Staphylococcus
Staphylococcus

Staphylococcus is a genus of Gram-positive Bacterium. Under the microscope they appear round , and form in grape-like clusters.The Staphylococcus genus include just thirty-three species....
, Streptococcus
Streptococcus

Streptococcus is a genus of sphere Gram-positive bacterium belonging to the phylum Firmicutes and the lactic acid bacteria group. Cell division occurs along a single Coordinate axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek language st?ept?? streptos, meaning easily bent or twisted,...
, Enterococcus
Enterococcus

Enterococcus is a genus of lactic acid bacteria of the Phylum Firmicutes. Members of this genus were classified as Group D Streptococcus until 1984 when genomic DNA analysis indicated that a separate genus classification would be appropriate....
, and Clostridium
Clostridium

Clostridium is a genus of Gram-positive bacteria, belonging to the Firmicutes. They are obligate anaerobes capable of producing endospores....
. It has also been expanded to include the Mollicutes, bacteria like Mycoplasma
Mycoplasma

Mycoplasma is a genus of bacterium which lack a cell wall. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis....
 that lack cell walls and cannot be Gram stained, but are derived from such forms. Actinobacteria
Actinobacteria

Actinobacteria or actinomycetes are a group of Gram-positive bacterium with high G+C ratio. ...
 are the other major group of Gram-positive bacteria, which have a high guanosine
Guanosine

Guanosine is a nucleoside comprising guanine attached to a ribose ring via a ?-N9-glycosidic bond.Guanosine can be phosphorylated to become GMP , cGMP , GDP and GTP ....
 and cytosine
Cytosine

Cytosine is one of the five main bases found in DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached ....
 content in their genomes (high G+C group). This contrasts with the Firmicutes, which have a low G+C content.

Both Gram-positive and Gram-negative bacteria may have a membrane called an S-layer
S-layer

An S-layer is a part of the cell envelope commonly found in bacteria, as well as among archaea. It consists of a monomolecular layer composed of identical proteins or glycoproteins....
. In Gram-negative bacteria, the S-layer is directly attached to the outer membrane
Outer membrane

The bacterial outer membrane is found in Gram-negative bacteria. Its composition is distinct from that of the cytoplasmic membrane - among other things, the outer leaflet of the membrane include a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and it is linked to the cell's peptidoglycan by Braun's lipoprotein....
. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Unique to Gram-positive bacteria is the presence of teichoic acid
Teichoic acid

Teichoic acids are polysaccharides of glycerol phosphate or ribitol phospate linked via phosphodiester bonds....
s in the cell wall. Some particular teichoic acids, lipoteichoic acids, have a lipid component and can assist in anchoring peptidoglycan, as the lipid component is embedded in the membrane.

Exceptions

The Deinococcus-Thermus
Deinococcus-Thermus

The Deinococcus-Thermus are a small group of bacterium comprised of cocci highly resistant to environmental hazards. There are two main groups....
 bacteria have Gram-positive stains, although they are structurally similar to Gram-negative bacteria.

Pathogenesis
Pathogenesis

The term pathogenesis means step by step development of a disease and the chain of events leading to that disease due to a series of changes in the structure and /or function of a cell/tissue/organ being caused by a microbial , chemical or physical agent....
 

Most pathogenic bacteria in humans are gram-negative organisms. Classically, six gram-positive genera are typically pathogenic in humans. Two of these, Streptococcus
Streptococcus

Streptococcus is a genus of sphere Gram-positive bacterium belonging to the phylum Firmicutes and the lactic acid bacteria group. Cell division occurs along a single Coordinate axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek language st?ept?? streptos, meaning easily bent or twisted,...
 and Staphylococcus
Staphylococcus

Staphylococcus is a genus of Gram-positive Bacterium. Under the microscope they appear round , and form in grape-like clusters.The Staphylococcus genus include just thirty-three species....
, are cocci (round bacteria). The remaining organisms are bacilli
Bacilli

Bacilli refers to a taxonomy Class of bacteria. It includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens like Bacillus anthracis ....
 (rod-shaped bacteria) and can be subdivided based on their ability to form spore
Spore

In biology, a spore is a reproduction structure that is adapted for biological dispersal and surviving for extended periods of time in unfavorable conditions....
s. The non-spore formers are Corynebacterium
Corynebacterium

Corynebacterium is a genus of Gram-positive, aerobic or Facultative anaerobic organism, non-motile, non-sporulated, rod-shaped actinobacteria. Most do not cause disease, but are part of normal human skin Flora ....
 and Listeria
Listeria

Listeria is a bacterial genus containing six species. Named after the English surgeon, Joseph Lister, Listeria species are Gram-positive bacilli and are typified by Listeria monocytogenes, the causative agent of listeriosis....
, while Bacillus
Bacillus

Bacillus is a genus of rod-shaped bacterium and a member of the division Firmicutes. Bacillus species are either obligate or facultative aerobes, and test positive for the enzyme catalase....
 and Clostridium
Clostridium

Clostridium is a genus of Gram-positive bacteria, belonging to the Firmicutes. They are obligate anaerobes capable of producing endospores....
 produce spores. The spore-forming bacteria can again be divided based on their respiration
Respiration

Respiration may refer to:* Respiration , the transport of oxygen to cells where cellular respiration takes place* Gas diffusion in soil, exchange of gases between plant roots and the atmosphere...
: Bacillus is a facultative anaerobe
Facultative anaerobic organism

A facultative anaerobic organism is an organism, usually a bacterium, that makes Adenosine triphosphate by aerobic respiration if oxygen is present but is also capable of switching to Fermentation ....
, while Clostridium is an obligate anaerobe
Obligate anaerobe

Obligate anaerobes are anaerobic organisms which fail to grow in the presence of oxygen.Obligate anaerobes die in presence of oxygen due to the absence of the enzymes superoxide dismutase and catalase which would convert the lethal superoxide formed in their cells due to the presence of oxygen....
.

See also

  • Gram-negative
    Gram-negative

    Gram-negative bacteria are those bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color....
  • Carboxydothermus hydrogenoformans
    Carboxydothermus hydrogenoformans

    Carboxydothermus hydrogenoformans is an extremely thermophilic Anaerobic organism Gram-positive bacterium that has the interesting property of producing hydrogen as a waste product while feeding on carbon monoxide and water....
Category:Gram positive bacteria


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