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16 Cards in this Set
- Front
- Back
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Define pathogenicity, virulence, virulence factors.
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Pathogenicity - the ability of m/o to cause disease
Virulence - the degree of pathogenicity Virulence factors = those properties an organism has that makes it virulent |
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What does bacterium have to do to cause disease?
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1. gain entrance into the body
2. adhere to tissue 3. avoid the host's defenses 4. damage host tissue |
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What are the three portals of entry into the host?
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1. Mucous membranes (respiratory tract, GI tract, genitourinary tract, conjunctiva/eyes)
2. Skin 3. Parenteral route (deposited directly into tissues beneath the skin or mucous membranes |
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How do m/o adhere to tissues?
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Adhesins (glycocalyx, fimbriae of Gram neg.).
1. Bacteria attach to host receptors 2. Attachment may be specific 3. Pathogens compete with normal flora for attachment 4. Some bacteria form a biofilm on a tissue (a microbial community that forms a slime layer on a surface) |
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How do m/o evade host defenses?
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Results in invasion of body.
1. Capsules (a virulence factor) 2. Certain cell wall components of some cells (M protein in Streptococcus pyogenes - are adhesins and are antiphagocytic) 3. Extracellular enzymes |
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What factors contribute to pathogenicity of some bacteria?
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Plasmids. R factors: plasmids that carry genes that encode proteins to make an organism resistant to one or more antibiotics. Other plasmids may code for virulence factors: staph enterotoxin, certain fimbriae of E.coli, tetanus toxin
Lysogenic Phage by coding for cirulence factors. Prophage beta in C.diphtheriae codes for the diphtheria toxin. A phage in Streptococcus pyogenes codes for the erythgenic toxin, a phage in Streptococcus pneumoniae codes for a capsule. |
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Leukocidins
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Extracellular enzyme/evade host defenses. Produced by some m/o when inside a white blood cell. Cause white blood cell to lyse.
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Hemolysins
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Extracellular enzyme/evade host defenses. Cause RBCs and WBCs to lyse.
Ex: Streptococci produce streptolysin O (SLO) and streptolysin S (SLS). Lyse RBCs and WBCs. |
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Coagulase
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Extracellular enzyme/evade host defenses. Clots fibrinogen in blood. Forms clot around cell. Protects cell from phage. Walls off m/o in boils.
Ex: Pathogenic S. aureus produces coagulase. |
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Bacterial kinases
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Extracellular enzyme/evade host defenses. Break down clots. Allows m/o to spread away from site of infection. Used therapeutically.
Ex: Streptokinase (fibrinolysin) produced by strep Staphylokinase produced by staph |
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Hyaluronidase
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Extracellular enzyme/evade host defenses. The spreading factor. Breaks down hyaluronic acid between cells of connective tissue. M/o penetrates tissue.
Ex: Clostridium perfringens produces hyaluronidase and causes gas gangrene. |
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Collagenase
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Extracellular enzyme/evade host defenses. Hydrolyzes collagen of connective tissue.
Ex: C. perfringens also produces collagenase |
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How do bacterial pathogens damage host cells
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1. Using host's nutrients (some bacteria sequester host's iron via siderophores)
2. Direct damage (some bacteria penetrate cet\rtain host cells that are nonprofessional phagocytes - ex: Shigella sp. and Salmonella sp. do this) 3. Toxin production (exotoxins and endotoxin) 4. Hypersensitivity reactions |
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What are exotoxins?
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Most are extracellular enxymes
Major virulence factor Coded for by plasmids or chromosome of cell Secreted by both Gram +/- May act away from site of organism Antigenic |
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What are three types of exotoxins (according to structure)?
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1. A-B toxins (type III toxins)
2. Membrane-disrupting toxins (type II toxins). Cause host membrane to lyse 3. Superantigens (type I toxins). Powerful protein antigens that stimulate T cells to release huge amounts of cytokines. |
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How are exotoxins classified and what are they?
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Classified according to body affected:
1. Neurotoxin - attack nerve cells 2. Hepatotoxins - attack liver cells 3. Enterotoxins act on the intestines 4. Cytotoxins affect a variety of cells |
