Bacteria

Gram Positive Bacteria

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Gram Positive Bacteria, Gram Stain Positive, Gram Positive Cocci, Gram Positive Rod, Gram Positive Spore-Forming Rod, Bacillus

  • See Also
  1. Bacteria
  2. Antibiotic
  3. Clostridium
  • See Also
  1. Bacteria
  2. Gram Negative Bacteria
  3. Anaerobic Bacteria
  4. Mycobacteria
  5. Intracellular Pathogen
  6. Antibiotic
  • 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)
  • Causes
  • Gram Positive Cocci
  1. Streptococcus (e.g. Streptococcus Pneumoniae)
    1. Gram+ Cocci arranged in pairs (e.g. Pneumococcus) or chains
    2. Catalase negative
  2. Staphylococcus (e.g. Staphylococcus Aureus)
    1. Gram+ Cocci arranged in clusters
    2. Catalase positive
      1. Catalase converts Hydrogen Peroxide (from Macrophages, PMNs) into water and oxygen
      2. Catalase positive organisms on a culture plate will bubble when exposed to Hydrogen Peroxide
  3. Enterococcus (Previously Group D Streptococcus)
  1. General
    1. Bacillus and Clostridium species may lie dormant as spores in harsh environments for years
    2. Bacillus and Clostridium species exert toxicity in humans via exotoxin release
    3. Bacillus species are aerobic, while Clostridium species are anaerobic
  2. Bacillus (aerobic)
    1. Bacillus anthracis (Anthrax)
    2. Bacillus Cereus
  3. Clostridium (anaerobic)
    1. Clostridium botulinum (Botulism)
    2. Clostridium tetani (Tetanus)
    3. Clostridium perfringens (Gas Gangrene)
    4. Clostridium sordellii (Clostridial Toxic Shock Syndrome)
    5. Clostridium difficile
      1. Recategorized as Clostridioides difficile in 2016
  1. Corynebacteria
    1. Corynebacterium diphtheriae (diptheria)
  2. Listeria monocytogenes
  3. Erysipelothrix rhusiopathiae
    1. Primarily a Zoonotic Pathogen (e.g. animal handlers)
  1. Actinomycetes
  • References
  1. Davis (1990) Microbiology, Lippincott, p. 21-50
  2. Gladwin (2014) Clinical Microbiology, Medmaster, Miami, p. 1 to 8