Streptococcus pyogenes Flashcards
General Properties
Group A
Encapsulated
Gram + cocci in chains
Beta hemolysis
Bacitracin sensitive
Secondary invader following viral infection
Where does it live?
oropgarynx and skin
Transmission
person to person by respiratory droplets
Direct contact with fomites
Diseases
Virulence Factors: Capsule
Made of hyaluronic acid. Hides strep from host because it resembles hist
Therefore antiphagocytic
Virulence Factors: M Protein
Adhesion
Antiphagocytic Prevents opsonins and binding
degrades C3b
Mimics cardiac myosin and causes antibodies to attack it
Virulence Factors: Streptococcal Pyrogenic Exotoxins (SPE)
3 types (A, B and C) A is most important
Produced by phage with lysogenic phage
Associated with toxic shock syndrome and scarlet fever
Virulence Factors: Streptolysin O
Lyses cells, including phagocytes
We generate antibodies (ASO antibodies)
Virulence Factors: Streptokinase
Lyses blood clots, facilitates spread
Converts plasminogen to plasmin
Suppurative Infections
Pharyngitis
Impetigo
Cellulitis (involves deeper layers of skin)
Erysipelas (more superficial) Most common cause
Necrotizing Fasciitis
Bacteremia and Sepsis
Pneumonia
Toxin Mediated Diseases
Scarlet Fever
Streptococcal toxic shock syndrome
Immune Mediated Diseases
Rheumatic fever (sequelae of throat infection alone)- Mitral valve
Post streptococcal glomerulonephritis PSGN(sequelae of throat or skin infection) 2 weeks after initial infection
