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43 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What would you see under the microscope for a gram stain slide with streptococci on it?
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gram-positive cocci
- tend to form chains |
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The catalase test for streptococci is...
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negative
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Do streptococci need oxygen?
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grow both aerobically and anaerobically
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What is the natural reservoir for streptococci pyogenes?
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- skin
- mucous membranes |
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What is the natural reservoir for strep viridans?
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- oropharynx
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What is the natural reservoir for E. faecalis?
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GI and Gu tracts
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What is the natural reservoir for S. agalactiae?
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- lower GI
- Female GU tract |
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alpha hemolysis is characterized by...
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a green zone
- bacteria have denature blood cells in the agar, but they aren't lysed |
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gamma hemolysis is characterized by...
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- no zone of clearing
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beta hemolysis is characterized by...
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- a clear zone, bacteria will lyse the blood cells
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what are lancefield group antigens?
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- tool to classify streptococci
- carbohydrate antigens in cell wall preparations used - how you get the name "Group A Strep" |
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Group A Strep
- species - hemolysis - diagnostic feature - diseases |
- S. pyogenes
- beta hemolysis - bacitracin sensitive - many diseases caused |
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Group B Strep
- species - hemolysis - diagnostic feature - diseases |
- S. agalactiae
- beta hemolysis - bactitracin resistant - neonatal meningitis, sepsis |
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Enterococcus
- lancefield group - hemolysis - diagnostic feature - diseases |
- D
- alpha, gamma - grows in high NaCl - endocarditis, UTI, nosocomial infections |
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Viridans
- lancefield group - hemolysis - diagnostic feature - human diseases |
- none
- alpha, beta, gamma - bile insoluble - lots of diseases |
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Strep pneumonia
- lancefield group - hemolysis - diagnostic feature - human disease |
- none
- alpha - bile solueble - pneumonia, sepsis, meningitis, otitis media |
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Pyogenic / suppurative diseases caused by group A strep
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- pharyngitis
- impetigo (skin rash) |
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pyrogenic diseases caused by group A strep
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- scarlet fever
- TSS - puerperal fever - sepsis |
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immunologic diseases caused by group a strep (downstream)
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- rheumatic fever
- acute glomerulonephritis |
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Three types of diseases caused by group a strep:
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1) pyogenic / suppurative
2) pyrogenic (fever response) 3) immunologic (downstream) |
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What are the traits of a successful pathogen?
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- enters host
- binds / adheres - gets nutrients and multiplies - spreads - evades the immune system - transmission to other hosts |
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This is a group a strep virulence factor that binds to fibronectin in the ECM.
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f-protein
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In order to adhere to respiratory epithelium, group a strep needs...
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F, a fibronectin binding protein
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Group A strep virulence factors that aid in immune evasion (4 of them)
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1) streptolysin O
2) C5a peptidase 3) M protein 4) hyaluronic acid capsule |
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streptolysin O
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- pore forming toxin
- targets neutrophils |
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C5a peptidase
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- cleaves C5a
- destroys chemotactic activity - evades complement cascade |
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M protein
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- helps to vary antigenic profile
- sequesters H factor and blocks C3 maturation - binds plasma fibrinogen and creates a thick shell around organism - blocks complement mediated phagocytosis - protects from MAC complex |
m = major
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Factor H
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- host protein that negatively regulates complement
- keeps C3 in off state so there is no opsonization or inflammation - binding correlates to invasiveness |
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How can you use M protein to attack bacteria?
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- m protein sticks out and is prone to Ab attack
- M protein-specific antibodies can be used to promote phagocytosis of group a strep |
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Does a capsule contribute to more or less invasive diseases?
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more invasive
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How is the capsule of group a strep turned on / off?
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- CovR/S on: capsule is shut off, will bind to fibronectin and form biofilms
- CovR/s off: capsule is ON, more invasive |
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How can group A strep lead to systemic toxicity?
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- streptococcal pyrogenic exotoxins
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How do superantigens work?
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- bind to conserved regions on MHC, will recruit nonspecific Tcells
- get amplification of T cells - Hyperreactive - SpeA and SpeC are superantigens from group A strep |
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Acute glomerulonephritis can follow...
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- either pharyngitis OR impetigo
- high attack rate (~40%) |
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Rheumatic fever can follow...
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- ONLY follows infections of pharynx
(only some people susceptible) |
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What causes rheumatic fever?
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- downstream non-suppurative consequence of GROUP A STREP
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Where is the natural reservoir for corynebacterium diptheriae?
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- respiratory tract of immune, asymptomatic humans
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Under a microscope diptheriae looks like?
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- gram positive
- club-shaped rod - often "v" formation |
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Diphtheriae is a classic ...... disease.
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TOXIN
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What is the mechanism of action of diptheria toxin?
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- will adp-ribosylate EF2
- inhibits protein synthesis - kills host cells (to get iron) - will ultimately get physical blockage of airways and tissue death |
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When is the toxin expressed vs. not expressed?
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- when iron plentiful = do NOT express toxin
- when iron scarce = EXPRESS TOXIN (want to kill cells and get their iron) |
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How is the toxin gene carried for diptheria?
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on a bacteriophage
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When might you see reemergence of diphtheria?
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- social strife with increased crowding, migration
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