Chapter 27HostmicrobeMed micro13th ed2

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Unformatted text preview: ck induced by toxic shock syndrome antigen of Staph Induce systemic reactions: fever, widespread clotting, shock EXOTOXINS: Based on SITE OF EXOTOXINS: Based on SITE OF ACTION: Cytotoxins: inhibit a cell function or cause cell death: Corynebacterium diptheriae: next slide Neurotoxins: inhibit nerve transmission (Cytolysins (Cytolytic toxins) are cytotoxins that cause cell death by lysis): Ex alpha toxin of Staph. Examples: tetanus and botulinum toxin Enterotoxins: alter permeability of intestinal epithelium Examples: Cholera and Staph aureus food poisoning enterotoxin (also superantigen) Diptheria toxin is an A-B toxin that inhibits a cell function: protein synthesis 1. B promotes binding of toxin to cell membrane 2. When it binds to cell membrane, it is cleaved and A is internalized. 3. A catalyzes ADP-ribosylation of elongation factor 2 (EF-2) and it no longer aids the transfer of amino acids to growing polypeptide chain. Ends protein synthesis Only a single toxin molecule is needed to kill a cell. Diptheria toxin is formed only by strains of Corynebacterium diptheriae cells that are lysogenized by phage beta. Lysogenic versus Lytic Lysogenic versus Lytic Staphylococcal alpha toxin: a pore forming cytotoxin that is produced by growing Staphylococcal cells Released as a monomer, 7 subunits oligomerize in cytoplasmic membrane forming a pore in target cell Pore releases the contents of cell allowing the influx of extracellular material & efflux of intracellular material Eukaryotic cells swell & lyse; in erythocytes, hemolysis Figure 21.18 Figure 21.18 Anthrax Anthrax Made of Three parts: each individual anthrax toxin protein is, in fact, nontoxic. A/B toxin. Actually A2B B component called protective antigen (PA) A components: Edema factor (EF): causes swelling Lethal factor (LF): causes cell death PA binds to anthrax receptor and then binds the EF & LF (Endocytosis brings complex into cell) Low pH of endosome causes conformation changes and allows EF & LF to enter cytosol and cause damage). Enzymatic activities lead to altered signaling pathways which cause macrophage functions to be impaired and ultimately apoptosis of the target cell. Botulinum toxin: o o o o o 7 distinct toxins­2 of which are encoded for by genes on lysogenic bacteriophages Toxin binds to presynaptic terminal membranes at nerve­muscle junction, blocking the release of acetylcholine required for transmission of nerve impulse to muscle. Muscle contraction inhibited & have flaccid paralysis 1 mg kills 1 million guinea pigs o Tetanus toxin: • 2 polypeptides, fixed to nerve synapsis (inhibitory interneurons), blocks release of glycine, a factor that induces muscle relaxation • Relaxation signal is blocked & paired muscles both contract • Spastic paralysis, twitching paralysis Exotoxins ­ Enterotoxins Exotoxins ­ Enterotoxins o Enterotoxins alters permeability of intestinal epithelium; causes massive secretion of fluid into the intestinal lumen causing diarrhea o o Staphylococcus aureus ­ vomiting, diarrhea: also super AG Vibrio cholera ­ • • • Cholera toxin: 3 polypeptides (A1, A2, B) B toxin involved in binding to ganglioside GM1 in e...
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This document was uploaded on 09/17/2013.

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