Gram Positive Bacteria

Aka: Gram Positive Bacteria, Gram Stain Positive, Gram Positive Cocci, Gram Positive Rods

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II. See Also

  1. Bacteria
  2. Gram Negative Bacteria
  3. Anaerobic Bacteria
  4. Mycobacteria
  5. Intracellular Pathogen
  6. Antibiotic

III. Pathophysiology

  1. Gram Positive Bacteria retain crystal violet stain (Gram Stain) on microscopy
    1. Thick peptidoglycan cell layer
      1. Surrounds the inner plasma membrane of Gram Positive Bacteria and retains crystal violet stain
    2. Contrast with Gram Negative Bacteria
      1. Relatively thin Peptidoglycan cell layer (does not retain the crystal violet stain)
      2. Gram Negative Bacteria are also surrrounded by an additional outer membrane
  2. Gram Positive Bacteria have two layers to their cell wall or envelope
    1. Outer Peptidoglycan cell layer
      1. Composed of repeated Disaccharides with a side chain of 4 Amino Acids
        1. Adjacent Amino Acid chains cross-link, and stabilize the peptidoglycan layer into a firm wall
      2. Transpeptidase (Penicillin binding Protein) is present in the inner cell membrane
        1. Transpeptidase is an enzyme that catalyzes Amino Acid cross-linking in the peptidoglycan layer
        2. Inhibited by Penicillin
    2. Inner cytoplasmic cell membrane
      1. Phospholipid bilayer with embedded Proteins (e.g. teichoic acid)

IV. Causes: Gram Positive Cocci

  1. Streptococcus (e.g. Streptococcus Pneumoniae)
  2. Staphylococcus (e.g. Staphylococcus aureus)
  3. Enterococcus (Previously Group D Streptococcus)

V. Causes: Gram Positive Rods

  1. Corynebacteria: Corynebacterium diphtheriae
  2. Listeria monocytogenes
  3. Bacillus anthracis (Anthrax)
  4. Erysipelothrix rhusiopathiae

VI. Causes: Gram Positive Branching Organisms

  1. Actinomycetes

VII. References

  1. Davis (1990) Microbiology, Lippincott, p. 21-50
  2. Gladwin (2014) Clinical Microbiology, Medmaster, Miami, p. 1 to 8

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