STREP

• Streptococcus


  Genus of gram-positive cocci arranged in pairs or chains, catalase negative, fastidious, most are facultative anaerobes, non-motile
• Streptococcus

  • Gram-positive
  • Cocci arranged in pairs or chains
  • Catalase negative
  • Fastidious; grown in enriched media
  • Most are facultative anaerobes
  • Non-motile but would just grow along the stab line or along the line of inoculation
• Hemolytic pattern on sheep's blood agar

  Alpha-Prime (α') – also known as Wide Zone: very small zone of NO HEMOLYSIS and then a wider zone of β-hemolysis, mistaken as β-hemolysis at first glance
• Lancefield classification

  • C carbohydrate present or extracted from the cell wall
  • Lancefield antigens are given letter names A, B, C, D, E, through S
  • More than 30 species of streptococci, only 5 are significant human pathogens
  • Three of these pathogens have Lancefield antigens: Lancefield group A, B and D
• Streptococcus pyogenes (Group A Beta-hemolytic Strep)


  • Pus-producing
  • Causes strep throat, scarlet fever, rheumatic fever, & post-streptococcal glomerulonephritis
  • Cell wall antigens: C carbohydrate, M protein (80 types) - major virulence factor that inhibits complement activation and protects from phagocytosis
• Exotoxins of Streptococcus pyogenes

  • Streptolysin O: antigen causing increased ASO titer, oxygen labile, destroys RBC & WBC
  • Streptolysin S: oxygen stable, also responsible for beta-hemolysis but not antigenic
  • Pyrogenic exotoxin/erythrogenic toxin: causes scarlet fever, streptococcal toxic shock syndrome
• Diseases caused by Streptococcus pyogenes

  1. Local invasion or exotoxin release: Streptococcal pharyngitis, Streptococcal skin infections, Scarlet fever, Streptococcal toxic shock syndrome

  2. Delayed antibody mediated diseases: Rheumatic fever, Glomerulonephritis
• Streptococcal pharyngitis

  • Classic strep throat: red swollen tonsils and pharynx, purulent exudate on tonsils, fever, swollen lymph nodes, usually lasts 5 days (penicillin therapy speeds recovery)
• Streptococcal skin infections

  • Folliculitis, cellulitis, impetigo
  • Erysipelas: infection of the dermis, raised bright red rash with sharp border
  • Necrotizing Fasciitis: flesh eating strep, break in skin, swelling, heat, redness that moves rapidly, skin changes to purple/blue, large blisters form, skin dies and muscle become infected
• Scarlet fever


  • Produced by pyrogenic toxin or erythrogenic toxin, fever, sore throat & scarlet-red rash beginning on trunk/neck then spreading to extremities, sparing the face, strawberry tongue
• Streptococcal toxic shock syndrome

  • Similar to scarlet fever, also mediated by the release of pyrogenic toxin, signs and symptoms are similar with staph TSS
• Rheumatic fever

  • Affects children 5-15 years, follows untreated streptococcal pharyngitis, 6 major manifestations: Fever, Myocarditis, Arthritis, Chorea, Subcutaneous nodules, Erythema marginatum
• Rheumatic fever


  Antigens in heart are similar to antigens of S. pyogenes, antibodies cross-react with heart antigens, most frequently damages the mitral valve, prophylactic penicillin therapy required
• Acute post-streptococcal glomerulonephritis

  • Antibody-mediated inflammatory disease of glomeruli, occurs 1 week after infection of pharynx OR skin by nephritogenic strains of S. pyogenes, antigen-antibody complexes deposited in glomerular basement membrane, child with puffy face, dark urine, hypervolemia, good prognosis
• Streptococcus agalactiae (Group B Strep)

  • Normal flora of lower GIT, 25% of women carry it vaginally, causes neonatal meningitis, pneumonia, sepsis in newborns
  • Early-onset infection: within 3 days, commonly associated with obstetric complications and premature birth, causes neonatal pneumonia
  • Late-onset infection: 1 week to 3 months, causes neonatal meningitis, uncommonly associated with obstetric complications
  • Virulence factors: Capsule, Sialic acid, Protease, Hemolysin, Hyaluronidase
• Streptococcus pneumoniae (Pneumococcus)


  • Major cause of bacterial pneumonia & meningitis in adults, otitis media in children
  • Appear as lancet-shaped, gram-positive cocci in pairs (diplococci)
  • Major virulence factor is its capsule, 84 different capsule serotypes
  • Causes chills, high fever, chest pain, shortness of breath, cough with yellow-green phlegm, alveoli fill with pus and bacteria
• Viridans group streptococci

  • S. salivarius, S. sanguis, S. mitis, S. intermedius, S. mutans
• Viridans group streptococci

  Most are alpha-hemolytic, normal flora of GI tract, nasopharynx and gingival crevices, cause dental infections, endocarditis, and abscesses
• Enterococcus

  • Normal flora of intestines, alpha hemolytic, cause urinary tract infections, biliary tract infections, one of the most common causes of nosocomial infections
• Group D Streptococcus

  S. bovis, S. equinus, association between S. bovis infection and colon cancer (50% of people with S. bovis bacteremia have a colonic malignancy)