Lecture 4-Toxins-Staphylococcus 2010

Toxin targets very well defined tissuescells

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Toxin targets very well defined tissues/cells ( V.cholerae, B.anthracis, C.tetani ) 2. Type III or Type IV secretion and toxins “injection” ( Yersinia, Shigella, Salmonella )
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ETEC/ V.cholerae LT-I, Cholera toxin
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Pathogenesis/Virulence Factors TTSS
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Lectures 4 & 5 Staphylococcus
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Classification Family Genus Species Staphylococcaceae Micrococcus, Staphylococcus, Alloiococcus S. aureus S. saprophyticus S. epidermidis S. lugdunensis S. haemolyticus
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Micrococcus and Alloiococcus Micrococcus -resemble staphylococci, can be confused with coagulase-negative staphylococci -may very rarely cause opportunistic infections Alloiococcus -only one species, A. otitidis , -implicated in chronic middle ear infections -slow grower, little studied
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Selection of medically important species Organism Historical Derivation Staphylococcus staphylé, bunch of grapes; coccus, grain or berry (grapelike coccus) S. aureus aureus, golden (golden or yellow) S. epidermidis epidermidis, outer skin (of the epidermis or outer skin)
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General Characteristics •Gram-pos. cocci, •Fac. anaerob Nonmotile •Support high salt (10% NaCl) Grow in grapes (“Staphyle =bunch of grapes) Staph vs. Strep
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Staph. aureus cell wall
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Cell Wall composition Capsule -expression depending on genetic factors and growth conditions -protects from phagocytosis by leukocytes - mediates adherence - diagnostic tool (serology); 11 capsular serotypes have been identified for S.aureus and mostly #5 and #7 associated with majority of infections
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Cell Wall composition Peptidoglycan -50% of cell wall weight! -highly crosslinked (unlike gram neg PG) -has endotoxin activity -Protein A and Teichoic acid are covalently linked to PG
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Peptidoglycan Penta-Glycine Crosslinking in S.aureus G= N-acetylglucosamine M=n-acetylmuramic acid Polysaccharide Polymer
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Cell Wall composition Teichoic Acid: -30-50% of cell wall dry weight -covalently linked to PG -is species specific (as in Streptococci) S. aureus ribitol teichoic acid (polysaccharide A) S. epidermidis glycerol teichoic acid (polysaccharide B)
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Teichoic Acid N=10-14 N Ribitol (shown) Or Glycerol (not shown) -covalently linked to PG Alternatively via lipid addition (=LTA) it can be anchored directly in cytoplasmic membrane
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Cell Wall composition Coagulase (“Clumping factor”): - Virulence factor of S.aureus - Binds fibrinogen and converts to insoluble fibrin (aggregation/clumping of bacteria) - S.aureus is ONLY Staph species expressing coagulase PRIMARY TEST for S. aureus is detection of coagulase !!
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