STREPTOCOCCUS

• Streptococci


  Gram-positive cocci (0.5 to 1.2um in diameter)

  
• Streptococci


  • Arrangement: Chains (Strep-) or Pairs (Dipplo-)
  • Non-motile
  • Non-spore forming
  • Facultative Anaerobes
  • Most are capnophiles (thrive in the presence of ↑ conc. of CO2)
  • Catalase-negative
  • Homofermentative (sole product of glucose fermentation: LACTIC ACID)
• Streptococci


  • Some are normal residents or agents of disease (humans/animals)
  • Others are free-living in the environment
• All streptococcal species are non-pigmented, except Streptococcus agalactiae which has a yellow, orange, or black-red pigment
• Primary pathogenic streptococcal species in humans

  • Streptococcus pyogenes
  • Streptococcus agalactiae
  • Streptococcus pneumoniae
• Classification of streptococci


  • Smith and Brown classification (based on hemolytic patterns)
  • Lancefield classification (based on antigen serogroupings)
  • Bergey's (academic) classification (based on temperature requirements)
• Bergey's (academic) classification of streptococci

  • Pyogenic group (do not grow at 10C and 45C, e.g. S. pyogenes)
  • Viridans group (not part of Lancefield's group, may be alpha-hemolytic or non-hemolytic, e.g. S. mutans, S. mitis, S. salivarus)
  • Lactic group (non-hemolytic, has a Lancefield N antigen, e.g. S. lactis)
  • Enterococcus group (formerly streptococci, indigenous to human intestine, e.g. E. faecalis, E. faecium)
• Hemolytic patterns in Smith and Brown classification

  • Beta-hemolytic (complete zone of clearing)
  • Alpha-hemolytic (greenish clearing of agar around colonies)
  • Gamma-hemolytic (no clearing of agar)
  • Alpha-prime (alpha surrounded by beta-hemolysis)
• Lancefield groupings of pathogenic streptococci


  • Group A - Streptococcus pyogenes
  • Group B - Streptococcus agalactiae
  • Group C - Streptococcus dysgalactiae subsp. dysgalactiae
  • Group D - Enterococcus species and non-enterococcus group D streptococci
  • Group F - Anginosus group streptococci
  • Group G - Anginosus group streptococci
• Streptococcus pyogenes


  • Group A beta-hemolytic streptococci
  • Encapsulated "HSN-K"
  • Not a normal flora, can colonize human throat and skin
  • Transmitted by direct contact, droplet, and foodborne (milk products, limited to children)
• Clinical diseases caused by Streptococcus pyogenes

  • Pharyngitis/Tonsilitis
  • Scarlet fever (scarlatina)
  • Streptococcal pyoderma (or impetigo)
  • Erysipelas
  • Cellulitis
  • Necrotizing fasciitis (streptococcal gangrene)
  • Puerperal fever
  • Bacteremia or sepsis

  
• Scarlet fever / scarlatina


  • Due to erythrogenic toxin
  • Starts with strep throat, occurs in association with streptococcal pharyngitis
  • Symptoms include strawberry tongue (due to hyperemia) and rashes starting at trunk and spreading to extremities

  
• Tests for scarlet fever

  • Dick's test (susceptibility test for immunity to erythrogenic toxin)
  • Schultz-Charlton test (diagnostic test detecting presence of erythrogenic toxin)
• Streptococcal pyoderma (or impetigo) is an infection of the superficial layers of the skin, often seen on the lower extremities and may also involve other pathogens such as S. aureus
• Erysipelas


  Infection of the dermis and subcutaneous tissues, characterized by reddening and thickening of skin and rapidly advancing brawny edema

  
• Cellulitis


  An acute, rapidly spreading infection of the skin and subcutaneous tissues, differentiated from erysipelas by the lesion not being raised and the line between involved and uninvolved tissue being indistinct
• Necrotizing fasciitis (streptococcal gangrene)


  Organism enters at the site of localized trauma or previous surgery, or via hematogenous seeding of subcutaneous muscles and soft tissue. Bacteria other than S. pyogenes can also cause it.

  
• Puerperal fever


  Occurs in women following childbirth (either by vaginal or abdominal/C-section) or abortion, infection of uterus and rest of reproductive tract
• Bacteremia or sepsis


  May result from streptococcal infection of traumatic or surgical wounds, can also occur with skin infections like cellulitis and rarely pharyngitis, can be rapidly fatal
• Post-streptococcal diseases


  • Acute rheumatic fever
  • Post-streptococcal glomerulonephritis

  
• Acute glomerulonephritis (AGN)


  Inflammation of the glomeruli of the kidneys caused by the M strains of S. pyogenes (nephritogenic), may be initiated by deposition and accumulation of antigen-antibody complexes on the glomerular basement membrane
• Rheumatic fever (RF)


  Considered the most serious sequela of S. pyogenes, results in damage to heart muscle and valves, an autoimmune disease where antibodies formed against streptococcal antigens cross-react with host heart tissue antigens

  
• Formation of Aschoff bodies, perivascular granulomas of the heart, is believed to be pathognomonic of rheumatic fever

  
• Virulence factors of Streptococcus pyogenes

  • Surface structures: Capsule, M protein, Protein F, Protein G
  • Toxins and enzymes: Streptokinase, Streptodornase, Hyaluronidase, Erythrogenic toxin, Hemolysin, Diphosphopyride nucleotidase
• Capsule


  Contains hyaluronic acid, anti-phagocytic (prevents phagocytosis by molecular mimicry), acts as an adhesin
• M protein


  Major virulence factor for rheumatic fever, imitates structure of heart tissue antigens, antigenically variable, anti-phagocytic, acts as an adhesin
• Protein F


  Fibronectin-binding protein, acts as an adhesin for attachment to pharyngeal epithelium
• Protein G


  Hinders antibody binding and phagocytosis
• Streptokinase


  Acts as a fibrinolysin, dissolves blood clots, used in management of thrombosis
• Streptodornase


  Acts as the microbe's DNAse, depolarizes and polymerizes DNA
• Hyaluronidase


  Destroys hyaluronic acid, acts as a "spreading factor" allowing bacterial dissemination into deeper tissues
• Erythrogenic toxin


  Also called streptococcal pyrogenic exotoxin, produced by lysogenized strains, causes streptococcal toxic shock syndrome and scarlet fever
• Streptococcal pyrogenic exotoxins


  • SpeA, SpeB, SpeC, SpeF
• Schultz-Charlton test


  Diagnostic test for scarlet fever, uses intradermal injection of anti-erythrogenic toxin to detect presence of toxin in the patient's system
• Dick's test

  Susceptibility test for scarlet fever, uses intradermal injection of diluted scarlet fever toxin to determine lack of immunity
• Streptococcal toxic shock syndrome


  Formerly called, streptococcal pyrogenic exotoxins (Spe)
• Streptococcal pyrogenic exotoxins


  • SpeA
  • SpeB
  • SpeC
  • SpeF
• Tests for streptococcal toxic shock syndrome

  • Schultz-Charlton Test
  • Dick's Test
• Schultz-Charlton Test


  Skin test for scarlet fever that uses antitoxin to the erythrogenic toxin of S.pyogenes subcutaneously: a positive reaction is blanching of the rash in the area around the injection site
• Dick's Test


  Skin test performed to determine an individual's susceptibility to scarlet fever. It consists of intradermal injection of diluted scarlet fever toxin on the arm of a suspected patient. Development of a red rash with a diameter of 10m or greater indicates lack of immunity to the disease