Streptococcus

Aka: Streptococcus, Beta-hemolytic Streptococcus, Alpha-hemolytic Streptococcus, Non-hemolytic Streptococcus, Lancefield Group

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II. Characteristics

  1. Gram Positive Cocci

III. Labs: Classification

  1. Hemolytic effect on Red Blood Cells (RBCs)
    1. Beta-hemolytic Streptococcus
      1. Beta-hemolytic streptococci completely lyse RBCs
      2. On a culture plate, colonies are surrounded by a clear zone of Hemolysis
    2. Alpha-hemolytic Streptococcus
      1. Beta-hemolytic streptococci partially lyse RBCs
      2. On a culture plate, colonies are stained green (Hemoglobin metabolite)
    3. Non-hemolytic Streptococcus
      1. No effect on Red Blood Cell lysis
  2. Lancefield Groups
    1. Renecca Lancefield subdivided streptococcal Bacteria into groups based on cell wall Antigens
      1. First isolated in the 1930s, from the milk of cows with bovine Mastitis
      2. Bacterial cell surface C Carbohydrate Lancefield Antigens
      3. Streptococci are classified as Group A, Group B, Group C, Group D... Group S
    2. Although historically used to differentiate Streptococci, more advanced methods are now used in practice
      1. Most Streptococcal species (>30 total) are not assigned Lancefield Antigens
      2. Only 3 of the significant streptococcal human pathogens have Lancefield Groups (A, B, D)

IV. Types: Beta-hemolytic Streptococcus

  1. General
    1. Beta-Hemolytic strep are also the source of several derived medications (e.g. Streptokinase, Hyaluronidase)
  2. Group A Streptococcus (Streptococcus Pyogenes)
    1. Causes Strep Throat, Scarlet Fever as well as respiratory infections and Cellulitis
    2. Complications include Rheumatic Fever, Toxic Shock, Glomerulonephritis, Reactive Arthritis and Henoch Schonlein Purpura
  3. Group B Streptococcus (Streptococcus agalactiae)
    1. Causes Group B Streptococcus Neonatal Sepsis (vertical transmission during delivery via vaginal colonization)
    2. Immunocompromised patients may also become infected with Group B Streptococcus (e.g. Pneumonia, Sepsis)
  4. Group C Streptococcus
    1. Normal human flora of the nasopharynx, skin, and genital tract, and rarely a cause for human infection
    2. Streptokinase
      1. Activates plasmin, triggering Fibrinolysis (nearly identical to staphylokinase)
      2. Streptokinase was extracted from Group C Strep to be used in MI and Stroke (prior to tPA, TNK)
  5. Group G Streptococcus

V. Types: Alpha-hemolytic Streptococcus

  1. Streptococcus Pneumoniae (Pneumococcus)
    1. Gram Positive Cocci in Pairs (Diplococcus), with no Lancefield Group assigned
    2. Polysaccharide Capsule protects it from Phagocytosis
      1. With infection, antibodies develop to capsule, but only protect against one of 84 serotypes
      2. Vaccines are polyvalent (21 of the most virulent serotypes as of 2024)
    3. Infections include Pneumococcal Pneumonia, Pneumococcal Meningitis, Otitis Media
  2. Viridans Streptococcus (Bacterial Endocarditis)
    1. Viridans is named for the greenish glow on culture media (Alpha-hemolytic Streptococcus)
    2. Subdivided into at least 5 sub groups
    3. Normal human colonization or the GI Tract and oropharynx
    4. Human Infections include SBE, Dental Infections and abscesses

VI. Types: Non-hemolytic Streptococcus (Gamma-Hemolytic)

  1. Certain members of Groups B, C, D, H, and O
  2. Group D Streptococcus
    1. General
      1. Gram-positive facultative anaerobic cocci
      2. Organisms colonize the human GI Tract as normal flora
      3. Hardy organisms that can survive in the harsh GI Tract, including 40% bile
      4. Extracellular Dextran allows binding to Heart Valves (Streptococcus Viridans, Group D Strep, Enterococcus)
    2. Non-Enterococcus
      1. Streptococcus equinus
      2. Streptococcus bovis
        1. Frequently found in patients with Colon Cancer
    3. Enterococcus
      1. Enterococcus was classified under Streptococcus
      2. Enterococcus was reclassified under its own genus as of 1984 following DNA analysis
        1. Enterococcus faecalis
        2. Enterococcus faecium

VII. References

  1. Patterson (1996) Streptococcus in Baron, Medical Microbiology, 4th ed., Galveston, Texas, chapter 13
    1. https://www.ncbi.nlm.nih.gov/books/NBK7611/

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