micro para lec

• Streptococcus


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


  • Hemolytic pattern on sheep's blood agar: Alpha-Prime (α') - very small zone of NO HEMOLYSIS and then a wider zone of β-hemolysis
  • Lancefield classification based on C carbohydrate present or extracted from the cell wall
• More than 30 species of streptococci, only 5 are significant human pathogens
• Significant human pathogenic streptococci

  • Lancefield group A
  • Lancefield group B
  • Lancefield group D
• Streptococcus pyogenes (Group A Beta-hemolytic Strep)


  • Major virulence factor is M protein which inhibits activation of complement and protects from phagocytosis
  • Produces exotoxins like Streptolysin O, Streptolysin S, Pyrogenic/Erythrogenic toxin
• Diseases caused by Streptococcus pyogenes

  • Local invasion or exotoxin release: Streptococcal pharyngitis, Streptococcal skin infections, Scarlet fever, Streptococcal toxic shock syndrome
  • Delayed antibody mediated diseases: Rheumatic fever, Glomerulonephritis
• Streptococcal pharyngitis


  Classic "strep throat" with red swollen tonsils and pharynx, purulent exudate, fever, swollen lymph nodes
• Skin infections by Streptococcus pyogenes


  Folliculitis, cellulitis, impetigo, erysipelas, necrotizing fasciitis ("flesh eating strep")
• Scarlet fever


  Produced by pyrogenic/erythrogenic toxin, causes fever, sore throat and scarlet-red rash
• Streptococcal toxic shock syndrome


  Similar to scarlet fever, also mediated by release of pyrogenic toxin
• Rheumatic fever


  Follows untreated streptococcal pharyngitis, not skin infections, affects children 5-15 years, has 6 major manifestations including fever, myocarditis, arthritis, chorea, subcutaneous nodules, erythema marginatum
• Acute post-streptococcal glomerulonephritis


  Antibody-mediated inflammatory disease of glomeruli, occurs 1 week after pharyngeal or skin infection by nephritogenic strains, causes puffy face, dark urine, fluid retention, high blood pressure
• Streptococcus agalactiae (Group B Strep)

  Normal flora of lower GI tract, 25% of women carry it vaginally, causes neonatal meningitis, pneumonia, sepsis
• Streptococcus agalactiae infections


  • Early-onset (first 3 days, usually 24 hours, associated with obstetric complications and premature birth, causes neonatal pneumonia)
  • Late-onset (1 week to 3 months, causes neonatal meningitis, less associated with obstetric complications)
• Virulence factors of Streptococcus agalactiae

  • Capsule (prevents phagocytosis), Sialic acid (most significant capsule component), Protease, Hemolysin, Hyaluronidase
• Streptococcus pneumoniae (Pneumococcus)


  Major cause of bacterial pneumonia and meningitis in adults, otitis media in children, appears as lancet-shaped gram-positive diplococci, major virulence factor is capsule
• Viridans group streptococci


  • S. mutans, S. salivarius, S. sanguis, S. mitis, S. intermedius
  • Cause dental infections, endocarditis, abscesses
• Enterococcus


  Normal flora of intestines, alpha-hemolytic, cause urinary tract infections, biliary tract infections, common cause of nosocomial infections
• Streptococcus bovis (Group D Strep)


  Association between S. bovis infection and colon cancer, 50% of people with S. bovis bacteremia have a colonic malignancy