Streptococcus pyogenes Flashcards
General Features
Gram + (long chain cocci)
Biochemical
Bacitracin Sensitive
Habitat
human skin and throat hence transmitted by direct contact or respiratory droplets
Virulence Factors
Capsule made of Hyaluronic Acid- allows to hide from the immune system
DNase and Ribonuclease- depolymerize DNA
Streptokinase- turns plasminogen into plasmin, activating fibrinolysis
Streptolysin-O (good Ag) and S (lysis of RBC, i.e. beta-Hemolysis, poor Ag) hemolysins
F protein- bind to fibronectin, help adhesion of the bacteria (together with M protein)
Clinical Features
S. Pyrogenic Exotoxins (Erythrogenic toxin)
Pharyngitis, tonsillitis, sinusitis, Impetigo, Erysipelas, and cellulitis
Acute Rheumatic Fever
Post-Strep Glomerulonephritis
S. Pyrogenic Exotoxins (Erythrogenic toxin) symptoms:
S. Pyogenes A, B, and C
Scarlet Fever (A/C)- “strawberry tongue”, pharyngitis (“strep-throat”) and diffuse rash that spares the face
Streptococcal Toxic Shock Syndrome (A and C, superantigens)
− Necrotizing Fasciitis (B)- “flesh-eating bacteria”
Acute Rheumatic Fever (post infection 2 weeks) criteria and sypmtoms
M protein: Molecular mimicry of the myosin in heart causing our own antibodies attack heart, especially the mitral valve, eventually leading to mitral stenosis
Anti-phagocytosis- inhibit opsonization (and also used to adherence)
Pharyngitis
criteria of RF symptoms:
• Joints- Polyarthritis
• Heart problems- Pancarditis (Endo-, Myo-, Pericarditis) and Valvular damage
• Subcutaneous Nodules on extensor surface, elbows and knees
• Erythema marginatum- rash with strict borders
• Sydenham’s chorea- rapid involuntary movement of hands and face
Post-Strep Glomerulonephritis signs
Glomeruli deposits from circulating Ab-Ag immune complexes (type 3 hypersensitivity)
Edema
“Cola-colored” urine
Diagnosis
Fastidious, shows Beta-Hemolysis on Blood agar (small pin-point colonies with huge lytic zone)
Anti-Streptolysin O (ASO)- measure antibodies titer against streptolysin-O, significant in RF
Treatment
Penicillin
