Chapter 27HostmicrobeMed micro13th ed2

Chapter 27HostmicrobeMed micro13th ed2

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Unformatted text preview: oughout host body Toxigenicity: toxins that inhibit host cell function or kill host cells. Two types: Exotoxins & Endotoxins Resistance: next chapter Acquired or Induced Immunity Humoral Immunity: mediated by antibodies Cellular Immunity: mediated by cells (T cells) Natural Resistance or Innate Immunity Cells: macrophages Mechanical Barriers: skin & mucous membranes Chemical Factors: interferon, fatty acids on skin Microbial Factors: Normal flora competition Virulence Factors: Invasiveness: ability of Virulence Factors: microbe to maintain presence and in many cases spread. Secreted enzymes—break physical barriers Physical characteristics—move, attach, hide Toxins­­poison Virulence Factors (Invasiveness) Secreted enzymes—break physical barriers 1.. 1 Hyaluronidase ­ This is also called the spreading factor because it catalyzes the breakdown of hyaluronic acid, the substance that cements the human cells together. This allows the bacterial cells to spread through tissue causing a condition known as cellulitis. [Staphyloccus,Streptococcus,Clostridia] Invasion of deeper tissue: Invasion of deeper tissue: Hyaluronidase = equals pathogen = equals hyaluronidase invasive pathogens reach hyaluronidase produced pathogens now invade deeper tissue epithelial surface S. pyogenes cellulitis Virulence Factors (Invasiveness) Secreted enzymes—break physical barriers 2.. 2 3. Coagulase­ This enzyme catalyzes the conversion of fibrinogen to fibrin with resultant clot formation. Present in pathogenic Staphyloccus. Fibrinolysin ­ This catalyzes the conversion of plasminogen to the fibrinolytic enzyme plasmin. Thus it acts opposite of coagulase. In Staphylococcus aureus, the gene for fibrinolysin is on a bacteriophage and is expressed during lysogeny. Virulence Factors (Invasiveness) Secreted enzymes—break physical barriers 4. Lipase: Production of excessive amounts of lipase 4. Lipase: allow bacteria to penetrate fatty tissue with the consequent formation of abscesses. 5. Collagenase: This enzyme catalyzes the degradation of collagen, a protein found in tendons, nails and hair. Virulence (Invasiveness) Virulence (Invasiveness) Continued 6. Leukocidins: cause lysis of white blood cells; Staphyloccus aureus Streptokinase and Streptodornase: actually fibrinolytic enzymes (category 3) 7. Lecithinase: destroys red blood cells & other tissue cells. 8. Hemolysins: lyse red blood cells Additional Virulence factors that promote invasiveness Physical characteristics—move, attach, hide 9. Capsule: carbohydrate or protein coat­adherence, antiphagocytic 10. Pili and fimbriae: attachment to surface receptors on host cells (urinary tract infections) 11. Flagella: motility Process of Spreading Out is Fundamental for Increased Process of Spreading Out is Fundamental for Increased Virulence of Some Microbes Invasiveness Group A Streptococci (GAS) are excellent examples Enzymes to breakdown clots: Streptokinase and Streptodornase (fibrinolytic) Enzymes to inhibit clotting machinery Strep throat → Necrotizing fasciitis (flesh eating bacteria) Necrotizing fasciitis is worst case Genetic predisposition? Severe disease may depend on immunogenetics of the...
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This document was uploaded on 09/17/2013.

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