Lecture 14.docx

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Medical Laboratory Science
Jenny Rhodes

MELS223 Lecture 14 8/21/2013 4:00:00 PM Toxin= microbial factor that damages the host Shia or Shiga-like toxins kill host cells by blocking protein synthesis Adhesion cell doesn’t damage deliberately. High local concentration of toxin is needed to damage cells. 3 different types of toxins 1. surface acting toxins. Acts on surface of human cell. Binds to receptor on plasma membrane and causes damage to human cell.  Super antigen 2. Pore-forming toxins. Puts holes in phagosome to help bacteria escape (Listerilysin). Others also put holes in membrane – plasma membrane.  Listeriolysin O 3. A/B toxins – have 2 components, A domain and B domain. Linked together in same protein and separated later on or actually separate toxins. A subunit has toxic activity. B subunit function is to bind to surface and help deliver A into cell. Diptheria toxin- exits from endosome and affects protein synthesis. Surface acting toxins  Superantigen  Ex. TSST  Made by Staphlylococcus aureus. Gram positive cocci, colonize skin and anterior nares. Disease: Skin infections, Medical implant associated infections, invasive disease (endocarditis), Necrotizing fasciitis – in blood stream. *Toxic Shock Syndrome TSS 20% of genes vary in different strains of same species of Staph aureus. Different virulence factors. Toxic Shock Syndrome  Tampon became colonized by S.aureus  TSST is a superantigen that stimulates T cells, causing uncontrolled cytokine (IL2) release, leading to septic shock 0 decreased tissue perfusion and oxygen delivery.  APC and TCR bind – T cell is stimulated to make cytokines and this is very specific – 1 in 10,000  When superantigen around – binds to both APC class II MHC and TCR, antigen does not have to be present and stimulates then without CD4 needed either! Cytokines produced a lot! Pore Forming Toxins  Large pore-forming toxins (20-30nm pores)  Extra cellular pathogens (L.monocyhtogenes – Listeriolysin O, C. perfringens – Perfringolysin O, S.pyogenes, S. pneumonia  Their receptor is cholesterol Small pore-forming txin: alpha-toxin (S.aureus)  Water rushes into cell as hypotonic environment, pressure inside cell builds and pops! Characteristics of alpha-toxin  Strains that make most alpha toxin are most virulent  Might be possible to use alpha toxin to make vaccines. Made it so that it can no longer make pores. Used to immunize mice, mouse generates antibodies against it.  Mice survived when injected w
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