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Virulence
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relative capacity of a microbe to cause damage in a host
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portals of entry
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mucous membranes, skin, parenteral route
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entering via the skin
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most microbes cannot penetrate unbroken skin; are some exceptions to this
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entering via mucous membranes
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respiratory, GI tract, genitourinary tract
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Entering Via The Placenta
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normally effective barrier form mothers organisms
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Entering Via The Parenteral Route
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allows circumvention of portal of entry; pathogens delivered deep to skin or mucous membrane
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Measure Of Virulence - ID50
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how many organisms needed to infect 50% of sample population; differs by microbe
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virulence factors
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properties of organism that enable virulence; enable adherence, evading host defenses, penetration, access to nutrients
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adherence
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enable attachment of microbe to the host; biofilms enable attachment; adhesion factors, adhesins, or ligands bind to receptors on host cells
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Evading host defenses
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evading phagocytosis; capsules, caogulases and biofilms resist phagocytosis; hiding inside host cell
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Evading antibodies
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antigenic variation; organism alters surface antigens after entry; antibody formation slow
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exoenzymes
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hyaluronidase, collagenase, kinase, IgA proteases
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hyalurinadase
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digests glue holding the cells together; blackening of tissue in wounds
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Collagenase
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breaks down collagen
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Kinase
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digests clots; organisms escape to invade
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IgA protease
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destroy IgA antibodies
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4 ways of causing disease
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utilizing host nutrients, causing direct damage, producing toxins, cause hypersensitivity reactions
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Utilizing host nutrients
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microbes need iron; siderophores; some have receptors for iron carriers
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causing direct damage
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pathogens utilize host cells for nutrients; produce wastes that damage cells; microbes divide inside cell; cell lysis may be caused
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toxins
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produced by some bacteria, algae, and fungi; transported by blood and lymph
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toxigenicity
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ability to produce a toxin
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Toxemia
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toxins in the blood
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Intoxication
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presence of toxin, not infection
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Potency of a toxin
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LD50: Lethal dose (of a toxin) for 50% of the test population
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bacterial exotoxins
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secreted inside and released; produced by both gram positive and negative; destroy cell parts or inhibit metabolic reactions; antitoxins
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antitoxins
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antibodies against toxin or toxoid
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Plasmids
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genes for pathogenicity
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Naming exotoxins
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by type of cell attacked; by disease caused; by bacterium
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types of exotoxins
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A-B toxins, membrane-disrupting toxins, and superantigens
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endotoxins
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only from gram-negative bacteria; Lipid-A; released upon bacterial death; endotoxins from different microbes produce same symptoms though not to same degree
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shock
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life threatening drop in BP; also result of cytokine release; septic shock from bacteria; endotoxic shock from gram negatives
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Endotoxin properties
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gram-negative; outer membrane; lipid; fever; large LD50
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LAL assay
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tests for endotoxins in drugs, medical devices, body fluids; uses blood of horseshoe crab
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portals of exit
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enables spread of disease; usually same as portals of entry; respiratory and GI; secretions; excretions; discharge; tissue shedding; coughing, sneezing, saliva, feces, urine
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