Streptococcus

Streptococcus

1. Lancefield classification

   • alpha hemolytic
     • S pneumoniae
     • viridans group
       • s. mutans
       • s. viridans
       • s. thermophilus
   • beta hemolytic
     • s. pyogenes (group A)
     • s. agalactiae (group B)
     • s. equi (group C)
   • gamma hemolytic
     • enterococcus species (group D)
     • lactococcus lactis (Group N)

2. S. pyogenes

   • characteristics
     • gram +
     • coccus
     • grows in chains
     • non motile
     • endospore forming
     • human specific
   • virulence factors
     • surface
       • M protein
         • binds Factor H of the complement system
           • factor H protects host cells from C3B deposition
         • many serotypes due to hypervariability of N terminus
       • hyaluronic acid capsule
         • mimics host cells
         • block opzonisation thru C3b
     • secreted
       • streptolysins
         • streptolysin O
           • is oxygen sensitive and can be seen under anaerobic conditions
         • streptolysin S
           • produces B hemolysis
       • super antigens
         • TSST 1
         • streptococcal pyrogenic exotoxins
           • SpeC
           • SpeI
           • aka scarlet fever toxins
   • Diseases
     • pharyngitis
       • swollen cervical lymph nodes
       • pus
       • Diagnoses
         • rapid strep test
           • + = antibiotics
           • - = throat culture
     • impetigo
       • highly contagious directly
     • scarlet fever
       • strawberry tongue
       • small red bumps on chest and stomach
       • happens with strep thoat
     • Rheumatic Fever
       • occurs 2-3 wks post infection (strep or scarlet)
       • caused by autoimmunity from antibody cross reactivity with M protein
       • acute rheumatic fever
       • rheumatic heart disease
     • Invasive Streptococcal disease
       • : isolation of s pyogenes from a normally sterile site
         • necrotizing faciitis (soft tissue)
         • necrotizing myositis (muscle)
         • streptococcal toxic shock syndrome
         • not bacterimia