BIOL_2051_ch25_notes - Chapter 25 Microbial Pathogenesis...

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Chapter 25 Microbial Pathogenesis Host-Pathogen Interactions Infection = entry of pathogen or parasite into a host Infection doesn’t always cause disease Most infections are removed by immune system Primary pathogens Have ability to penetrate host defenses Opportunistic pathogens Cause disease only in compromised host (possible compromises): Immune system defective Break in tissue allows organism access to new site Loss of other microflora allows organism to bloom Pathogenicity of organism Measure of ability to cause disease Determined by genetic makeup of organism Infectious dose = ID 50 Number of organisms to colonize 50% of host population Virulence Rate of lethal infections Lethal dose – LD 50 Number of organisms needed to kill 50% of host Infection Cycle Spread by direct contact Spread by indirect contact Contact with fomites – inanimate objects that can carry infectious microbes (elevator buttons, etc)
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Horizontal transmission via vectors (organisms that carry infectious microbes) Mosquitoes— yellow fever, malaria (ex. of vector) Reservoir for disease organism (reservoir carries microbe but is not diseased by it) May not show disease symptoms Mode of entry depends on pathogen Mucosal surfaces, wounds, insect bites Virulence Factors Virulence genes Encode factors allowing pathogen to invade host Toxins, attachment proteins, capsules Pathogenicity islands Section of genome Contain multiple virulence factors Often encode related functions E.g., protein secretion system, toxin production Transferred as a block from other organisms (like transferring plasmids to other org.)
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BIOL_2051_ch25_notes - Chapter 25 Microbial Pathogenesis...

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