Cards (14)

  • Streptococci can be classified based on their general features:
    • Gram positive
    • Non-motile
    • Catalase negative
    • Ovoid to spherical in shape
    • Form pairs or chains
    • Aerotolerant / Facultative anaerobes
    • Grow on blood enriched medium
  • Streptococci can be classified in two ways:
    • Hemolytic properties on blood agar
    • Serologic (Lancefield) groupings
  • Hemolytic properties on blood agar:
    • α-Hemolytic: results in a green pigment ring around the colony due to a chemical change in hemoglobin
    • β-Hemolytic: results in gross lysis of RBCs, creating a clear ring around the colony
    • γ-Hemolytic: no color change or lysis of RBCs
  • Serologic (Lancefield) groupings:
    • Many streptococci have a polysaccharide in their cell walls known as C-substance
    • Classifies primarily β-hemolytic streptococci into groups A through U based on their C-substance
    • Clinically important groups are A and B
  • Group A β-Hemolytic Streptococci (S. pyogenes):
    • Most clinically important member of this group
    • Can cause rheumatic fever, acute glomerulonephritis, cellulitis, tonsillopharyngitis, impetigo, erysipelas, puerperal sepsis, toxic shock syndrome
    • Post-streptococcal sequelae include acute rheumatic fever and acute glomerulonephritis
    • Identified using rapid latex antigen kits
    • Treatment includes penicillin, clarithromycin or azithromycin, and clindamycin
  • Group B β-Hemolytic Streptococci (S. agalactiae):
    • Found in vaginocervical tract of female carriers, urethral mucous membranes of male carriers, and GI tract
    • Can be transmitted sexually and from mother to infant
    • Causes meningitis and septicemia in neonates
    • Also causes infections in postpartum women and individuals with impaired immune systems
    • Identified through latex agglutination tests
    • Sensitive to penicillin G and ampicillin
  • Streptococcus pneumoniae (Pneumococcus):
    • Gram-positive, nonmotile, encapsulated cocci
    • Common cause of community-acquired pneumonia, adult bacterial meningitis, otitis media, sinusitis, and mastoiditis
    • Cultured on blood agar
    • Releases α-hemolysin that damages red cell membranes
  • Streptococci can be classified based on their general features:
    • Gram positive
    • Non-motile
    • Catalase negative
    • Ovoid to spherical in shape
    • Arranged in pairs or chains
    • Aerotolerant / Facultative anaerobes
  • Streptococci can be classified in two ways:
    • Hemolytic properties on blood agar
    • Serologic (Lancefield) groupings
  • Hemolytic properties on blood agar:
    • α-Hemolytic: results in a green pigment ring around the colony due to a chemical change in hemoglobin
    • β-Hemolytic: results in a clear ring around the colony due to gross lysis of RBC
    • γ-Hemolytic: causes no color change or lysis of RBC
  • Serologic (Lancefield) groupings:
    • Many streptococci have a polysaccharide in their cell walls known as C-substance
    • Classifies primarily β-hemolytic streptococci into groups A through U
    • Clinically important groups are A and B
  • Group A β-Hemolytic Streptococci (S. pyogenes):
    • Most clinically important member of this group
    • Can cause rheumatic fever, acute glomerulonephritis, cellulitis, tonsillopharyngitis, impetigo, erysipelas, puerperal sepsis, toxic shock syndrome
    • Post-streptococcal sequelae include acute rheumatic fever and acute glomerulonephritis
    • Identified through rapid latex antigen kits
    • Treatment includes penicillin, clarithromycin or azithromycin, and clindamycin
  • Group B β-Hemolytic Streptococci (S. agalactiae):
    • Found in vaginocervical tract of female carriers, urethral mucous membranes of male carriers, and GI tract
    • Can be transmitted sexually and from mother to infant
    • Leading cause of meningitis and septicemia in neonates
    • Also causes infections in postpartum women and individuals with impaired immune systems
    • Identified through latex agglutination tests
    • Sensitive to penicillin G and ampicillin
  • Streptococcus pneumoniae (Pneumococcus):
    • Gram-positive, nonmotile, encapsulated cocci
    • Lancet shaped, occurring in pairs
    • Common cause of community-acquired pneumonia, adult bacterial meningitis, otitis media, sinusitis, and mastoiditis
    • Cultured on blood agar
    • Releases α-hemolysin that damages red cell membranes