streptococci

• 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