Streptococci

Morphology

Gram Positive Cocci
Arranged in chains
- Think Streptococcus throat like necklace
May elaborate capsular polysaccharide that impedes phagocytosis » Slime
Pili project from capsule

Classification

ß-Haemolytic
- Produce Haemolysins
- Group A
  - Streptococcus pyogenes
  - Majority of pathogens
- Group B (B = Baby)
  - Streptococcus agalactinae
  - Normal flora of female genital tract
  - Important in neonatal infections
- Group G (G = Gut)
  - Normal enteric flora
    - Enterococcus
    - Streptococcus faecalis
    - Streptococcus faecium
Non-ß-Haemolytic
- Streptococcus pneumoniae
  - Cause pneumonia
- Streptococcus Viridans
  - Normal respiratory flora
- Peptostreptococci
  - Gut Anaerobes

Toxins/ Enzymes

Haemolysins
- Haemolyse RBC
  - Incomplete disruption – Alpha haemolysis
  - Complete disruption – Beta haemolysis
- Group A – ß-Haemolytic Strep produce
  - Streptolysin O
    - Streptolysin S
Streptokinase
- Converts Plasma Plasminogen to Plasmin
- Proteolytic enzyme that digests fibrin
Hyaluronidase
- Splits Hyaluronic acid
- Aids in spreading infection
Erythrogenic Toxin
- Causes rash of Scarlet Fever

Pathology

ß-Haemolytic Streptococcus
Commonly cause
- Erysipelas
- Strep Throat
- Impetigo
- Infective Endocarditis (SBE)
- Rheumatic Fever
- Acute Glomerulonephritis

Treatment

All sensitive to Penicillin G