Streptococcus Flashcards
Streptococcus general characteristics (6):
- Gram positive.
- Cocci arranged in pairs or chains.
- Non-motile.
- Facultative anaerobic or capnophilic.
- Catalase negative.
- Complex nutritional requirements: blood or serum enriched media for isolation.
Streptococcus pyogenes (7):
Group A Streptococcus
- Gram positive.
- Facultative anaerobe.
- Capsule (hyaluronic acid).
- Beta-hemolytic.
- M-proteins (80 types).
- F-protein bind fibronectin.
- Bacitracin sensitive.
Major virulence factors for group A Streptococcus (8):
- Capsule.
- M proteins.
- C5a peptidase.
- DNase.
- Streptolysin O and S.
- Hyaluronidase.
- Streptokinase.
- Pyrogenic/erythrogenic exotoxins.
Biological actions of strep pyogenes capsule:
Non-immunogenic and anti-phagocytic.
Biological actions of C5a peptidase:
Anti-chemotactic and reduces inflammation mediated by C5a.
Biological actions of streptokinase:
Promotes bacterial spread into tissues by breaking down blood clots.
Streptolysin O (2):
Oxygen labile
- Lyses leukocytes, platelets and erythrocytes.
- Immunogenic, indicating a recent GAS infection (ASO test).
Streptolysin S (4):
Oxygen-stable
- Lyses leukocytes, platelets and erythrocytes.
- Stimulates release of lysosomal enzymes.
- Beta-hemolysis.
- Non-immunogenic.
DNase (4):
- Four distinct forms (A, B, C, D).
- Anti-DNase B: Important marker of cutaneous GAS infection especially in those who failed ASO test.
- Depolymerizes cell free DNA in pus (reduction of viscosity).
- Contributes to spread from local site.
Suppurative streptococcal diseases (5):
- Pharyngitis.
- Scarlet fever.
- Impetigo.
- Cellulitis (#1).
- Erysipelas.
Scarlet fever (3):
- Occurs when the infecting strain is lysogenized by a bacteriophage that produces a pyrogenic exotoxin.
- Red maculopapular rash on trunk –> extremities.
- White and red “strawberry” tongue.
Impetigo (2):
Purulent with crusting
- Colonization is due to direct contact with an infected person or fomites.
- Regional lymph nodes enlarged but lack systemic signs.
Erysipelas (2):
- Localized pain, inflammation, lymph node enlargement and systemic signs.
- Historically on the face but becoming more common on the legs.
Non-Suppurative streptococcal disease (2):
No GAS present.
- Acute glomerular nephritis.
- Acute rheumatic fever.
Acute glomerular nephritis (4):
AGN
- Acute inflammation of renal glomeruli with edema, HTN, hematuria and proteinuria.
- Post-pharyngitis or post-skin infection (after resolution).
- Facial edema, smoky urine.
- Type III hypersensitivity.
Acute rheumatic fever (5):
ARF
- Pancarditis.
- No GAS present.
- Post pharyngitis only.
- Due to cross-reactivity of anti-M protein antibody with human cardiac tissue.
- JONES symptoms.
Streptococcus agalactiae (7):
Group B Streptococcus
- Gram positive.
- Cocci in pair.
- Capsule.
- CAMP test positive.
- Beta-hemolytic.
- Threat to infants infected perinatally.
- Responsible for post-partum endometritis.
Streptococcus agalactiae virulence factors (2):
- Capsule.
- Sialic acid - capsular component, inhibits alternate pathway of complement.
Streptococcus pneumoniae (8):
- Gram positive.
- Cocci in pairs or short chains.
- Capsule.
- CAMP test negative.
- Bile soluble (bile causes lysis).
- Aerobically alpha-hemolytic; anaerobically beta-hemolytic.
- Catalase negative.
- Optochin sensitive.
Streptococcus pneumoniae virulence factors (5):
- Capsules.
- Robust biofilm formation.
- IgA proteases cleaves IgA.
- Ahesins - mediate attachment to epithelial cells.
- Pneumolysin - destroys the ciliated epithelial cell.
Streptococcus pneumonia infections (4):
MOPS
- Meningitis (#1 adult).
- Otitis media (#1).
- lobar Pneumonia (#1 adult).
- Sinusitis (#1).
Enterococcus (8):
- Gram positive.
- Catalase negative.
- Bacitracin resistant.
- Variable hemolysis.
- Can grow in up to 6.5% NaCl.
- Bile resistant.
- Can hydrolyze esculin.
- Cocci in pairs or short chain.
Enterococcus virulence factors (5):
- Aggregation substance.
- Carbohydrate adhesins.
- Cytolysin - inhibits gram positive bacteria and induces local tissue damage.
- Gelatinase.
- Antibiotic resistant.
Streptococcus viridans (7):
- Gram positive.
- Alpha hemolytic.
- Optochin resistant.
- No Lancefield antigens.
- Sub-acute endocarditis (#1).
- Dental carries.
- Normal flora of mouth and teeth.
