BIO 226T - Lecture 10 Study Questions

BIO 226T - Lecture 10 Study Questions - Lecture 10 Study...

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Lecture 10 Study Questions 1. Toxin – a microbial product or component that can injure another cell or organism at low concentrations. Toxins may be proteins, lipids, or other substances. 2. Exotoxins Endotoxins Gram + and Gram – bacteria Only Gram – Secreted from cell Not secreted from cell Polypeptide – proteins only Lipopolysaccharide (LPS) Genes in plasmid or bacteriophage Genes in bacterial chromosome High toxicity (fatal dose = 1 μg) Low toxicity (fatal dose = hundreds of μg) Alter cell function (cholera toxin), kill cells (diphtheria toxin), and generalized effects (shock, death) Generalized clinical effects (fever, shock, death) ADP-ribosylation, superantigen, protease, lecithinase TNF-α (tumor necrosis factor alpha) and interleukin-1 Induces high-titer antibodies (aka antitoxins) Poorly antigenic Toxoids used as vaccines No vaccine available Destroyed rapidly at 60 C (except staphylococcal enterotoxin) Stable at 100 C for one hour Causes tetanus, botulism, diphtheria Causes meningococcemia, sepsis by Gram – rods 3. Cytotoxin – affect general tissue (i.e. diphtheria toxin) Enterotoxin – affect gastrointestinal cells (i.e. cholera toxin) Neurotoxin – affects nerve tissue (i.e. botulinum and tetanus toxins) 4. Producing an exotoxin in vivo gives the pathogen an “edge” in the infectious process because it makes it easier for the toxin to spread to the bloodstream and cause a more serious infection. Four major mechanisms of action of exotoxins: 1) Exotoxins that are degradative enzymes – used by some invasive bacteria to spread through tissue Ex. Staphylococcal exfoliatin toxin splits intercellular bridges in epidermis top layer of skin to “peel off like a peach” Staphylococcal Scalded Skin Syndrome Ex. Pyrogenic exotoxin B (from Group A streptococci, “flesh-eating bacteria”) is a serine protease that rapidly destroys tissues necrotizing fasciitis 2) Exotoxins that disrupt host cell membranes – damage host cytoplasmic membranes lysis of cells (includes body cells, RBCs, and phagocytic WBCs before they have a chance to engulf and destroy pathogens); directly damage body cells at site of infection contributes to disease and facilitates pathogen spread a) enzymatically lyse host cell membranes – i.e. alpha toxin of Clostridia spp. , a phospholipase destroys lecithin component of membrane
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This note was uploaded on 03/19/2008 for the course BIO 226T taught by Professor Field during the Fall '06 term at University of Texas at Austin.

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BIO 226T - Lecture 10 Study Questions - Lecture 10 Study...

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