Streptococci I Flashcards
Streptococci anaerobic or aerobic?
Facultative anaerobes (can grow in both)
a, b, y hemolysis
a - partial hemolysis ex: viridans streptococci, streptococcus pneumoniae b - total hemolysis, no intact RBCs (groups A,B, C, and G, sreptococcus iniae) y - not really hemolysis (strep gallolyticus, enterococcus, milleri group)
How to differentiate between a streptococci?
Strep pneumoniae are susceptible to optochin (death disc) and soluble in bile salts while viridans strep are not
How to differentiate between b-hemolytic strep?
Susceptibility to bacitracin (s pyogenes is suseptible while others group B, C, and G are resistant) when you think B-hemolytic strep…use the B (bactracin) test!
What does Lancefield classification rely on?
immunologic classification based on differences in cell wall carbohydrates (Groups A, B, C, D, F and G)
Hyaluronic acid capsule
non-antigenic (indistinguishable from human connective tissue hyaluronate). antiphagocytic (interferes with PMN phagocytosis)
M proteins
immunologically distinct group A, exist on fimbriae, antiphagocytic prevents complement
C- carbohydrate
group polysaccharide, basis of Lancefield groupings,
Lipoteichoic acid
functions as adherence ligand
Muramyl dipeptide
aka peptidoglycan - phage receptor, endotoxin-like activity
Pyrogenic exotoxins A, B, C, D) aka erythrogenic toxins aka SPEA, SPEB, SPEC etc,
toxins responsible for scarlet fever rash….antibodies to these protect against repeat infection
Streptolysin O
oxygen-llabile hemolysin that is neutralized by cholesterol in skin. Anti titers used to Dx rheumatic fever, less useful following skin infections
Streptokinase
activates plasminogen to disrupt blood clots (can be used therapeutically in patients with coronary artery occlusion)…not really used much anymore since you can get allergic rxns
Hyaluronidase
contributes to pathogenicity by allowing spread of infection through tissues
DNAse
antigenic, antiDNAse used dx after skin infections
Which class of MHC are presented by APCs and cleaved into peptides
Class II MHC
How can streptococcus pyogenes cause disease?
- direct infection with tissue destruction - toxin production - immunological response
pharyngitis/tonsillitis (“strep throat”)
-abrupt onset of sore throat with malaise, fever, and headache -edema and lympphoid hyperplasia, tonsil exudates, enlarged nodes, temperature greater than 101F
What is the “gold standard” for dx of strep throat?
Throat culture! can also use rapid antigen tests
Scarlet fever
“strawberry tongue”, “sandpaper rash”, results from infection due to strain of S. pyogenes that produces erythrogenic toxin as a consequence of being infected by a page
Pyoderma (impetigo)
superficial skin infection with papule-vesicle-pustule crust stages due to S pyogenes, S aureus…spreads within households on fomites
Cellulitis
vast majority due to S pyogenes. Diffuse inflammation of both skin and subcutaneous tissues with redness and tissue edema
lymphangitis
charactersitic of S pyogenes soft tissue infections, lymph node tenderness may precede soft tissue symptoms
erysipelas
form of celluitits characterized by diffuse lymphangitis in which infection actively spreads along lymphatics with redness and pain at advancing margins
