B-haemolytic streptococci Flashcards
Are streptococci gram positive or negative?
Gram positive
How are streptococci classified?
By haemolysis
Which class of streptococci completely break down red blood cells?
Beta
What is an example of alpha haemolytic streptococci?
Strep pneumoniae
What is an example of beta haemolytic streptococci?
Streptococcus pyogenes
What lancefield group is strep pyogenes?
Group A
What are the streptococcus pyogenes virulence factors?
Hyaluronic acid capsule, M protein, adhesins, streptolysins O and S, dnases, hyaluronidase, streptokinase, streptococcal pyrogenic exotoxins
What is the action of the hyaluronic acid capsule on strep pyogenes?
Inhibits phagocytosis by neurophils and macrophages - similar to human connective tissue
What is the action of M protein?
Resist phagocytosis by inhibiting activation of alternative complement pathway
What is action of adhesis eg lipoteichoic acid?
Adherence
What are the actions of streptolysins O and S?
Lysis of erythocytes, neutrophils, platelets
What are the actions of Dnases A, B, C ad D?
Degradation of DNA
What is the action of hyaluronidase?
Degradation of hyaluronic acid in connective tissue
What is the action of streptokinase?
Dissolution of clots through conversion of plasminogen to plasmin
What is the action of streptococcal pyrogenic exotoxins?
Cleaves IgG bound to group A strep
What are some complications of strep pharyngitis?
Scarlet fever (due to infection with strep pyrogenic exotoxin strain of s pyogenes)
Peritonsillar cellulitis/abscess
Sinusitis, otitis media, meningitis
Acute rheumatic fever
Acute post-strep glomerulonephritis
What are some strep pyogenes skin infections?
Impetigo, erysipelas, cellulitis, necrotising fasciitis
What causes strep toxic shock syndrome?
Entry of group A strep into deeper tissues and bloodstream
Exotoxins stimulate T cells through binding to MHC class II APC and TCR
M protein fibrinogen complex formation
