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Name the 3 genera (we were taught...)
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StreptococcusStaphylococcusCorynebacteria
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Shape and growth pattern of streptococcus. Relationship to oxygen...
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Sperical or ovoid bacterium, grows in pairs or chains. (chains particularly when cultured). Facultatively anaerobic
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What is the significance of Lancefield? What letters are involved? What (chemically) is it based on?
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One method of serotype classification. Gives A-H and K-V, based on COH cell-surface antigens. Not all are medically significant.
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Which Lancefield serotypes are particularly significant and what species do they correspond to?
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For differentiation of strep species/ groups. Lancefield group A - strep pyogenesGroup B - Strep agalacticae (cause of neo-natal infections)
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What is the serotyping for Strep Pyogenes?
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Griffith type (M and T)
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5 common strep pyogenes infections
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Tonislitis (strep throat)Otitis mediaWound infections (which can lead to cellulitis)Impetigo (blisters, sores, can be more serious. Look it up....)scarlet fever (massive immune response to a strep super-antigen)
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Complications of scarlet fever (*2)
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Glomerulonephritis (type III hypersensitivity reaction)Rheumatic fever (believed to be a type II reaction by antibodies raised against the strep exotoxin attacking tissues in the heat, skin and brain)
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Antibiotic of choice against strep pyogenes
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Penicillin
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Explain the three types of haemolysis
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Alpha - changes Hb to the green met-haemaglobin through reaction of H2O2Beta - lysis of erythrocytes by pore-forming toxins such as streptolysin O and S. Gamma - no haemolysis
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Virulence factors for strep pyogenes (x7 - sorry!)
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- Hyalouronic acid capsule - non-antigenic- Hyalouronidase - aid spread of bacterium by breaking down its capsule- Streptolysin O - pore-forming toxin that binds to cholesterol and causes lysis of RBCs. Highly antigenic. Anti-SLO test diagnostic for strep infection.- Streptolysin S - similar to streptolysin O but non-antigenic- Protein M - antiphagocytic surface protein- streptokinase - breaks down clots- C5a peptidase - breaks down complement
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4 pathogenic strep species (NB, one class of species)
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Streptococcus pyogenesStrep agalacticaeStrep pneumoniaeViridans streptococci (actually a class of oral strep including strep oralis and strep sanguinis) - can cause systemic / mileri infections when they get into the wrong place (endocarditis, etc.)
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Features of streptococcus pneumoniae: - appearance on agar - haemolysis (plus explanation) - they're soluble in something....
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Grows in glossy colonies on agaralpha-haemolytic (produces H2O2)bile soluble
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Prevalence / mortality of strep pneumoniae
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Commensal in about 30% of the populationCauses disease in about 1 per 1000 population /yearMortality of 10-20%
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What else does strep pneumoniae significantly cause besides 20% of cases of CAP? (x3)
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About 20% of cases of meningitisSinusitisOtitis media
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Why are asplenic pts at higher risk of infection by strep pneumoniae?
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Spleen produces tuftsin - opsonisation protein
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