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Pathogens
Microorganisms capable of causing infectious diseases
Pathogenicity
ease with which a pathogen can cause disease
Virulence
relative degree of damage caused by a pathogen
ID50
Infectious dose that is required to give a definite symptomatic infection in 50% of the inoculated recipients
LD50
lethal dose required to KILL 50% of the inoculated recipients in a given length of time
Portal of Entry
Route by which a pathogen enters our body
Portal of Exit
Usually related to the site of the body where the pathogen replicated to cause disease
Invasive pathogens
have the ability to colonize and invade or spread through normally sterile body tissues
Toxigenic pathogens
produce exotoxins and/or endotoxins that cause toxic effects on host cells
Adherence
Mechanism bacteria use to attach themselves to the host tissue
Bacterial adhesions/ligands proteins
present at the tips of fimbria or pili
Extracellular slime layers or biofilms
used for virulence factors and adherence to artificial implants like catheters
Bacterial capsules
function as virulence factors by preventing phagocytosis. (Streptococcus pneumoniae)
opsonins
molecules that enhance phagocytosis
Antigenic variation
countering effects of opsonic antibodies by producing many antigenically distinct forms of capsules
Invasin Proteins
When produced by some enterics, they facilitate adherence to M cells of colon.
Mucous Membranes (portal of entry)
GI tract, Respiratory tract, Genital tract
Skin (portal of entry)
-Unbroken skin is impenetrable -Hair follicles and sweat glands
Parental Route (Portal of entry)
Direct inoculation into the skin or mucous membrane
Organotropism
ability to infect certain tissues (that express receptors for adhesions)but not other tissues (those lack receptors for adhesions)
adsorption proteins
initiate infection of susceptible target cells (e.g. HIV gp120 binds CD4 on T cells).
M protein
resists phagocytosis
Opa protein
inhibits T helper cells
Mycolicacid
(waxy lipid)resists digestion
Kinases
Digest fibrin clots
Coagulase
Coagulates fibrinogen (Forms a Fibrin Clot)
Hyaluronidase
Hydrolyzes hyaluronic acid (Digests Hyaluronic acid)
Collagenase
Hydrolyzes collagen (Breaks down collagen)
IgA protease
Destroy IgA antibodies
Leukocidins
Enzymes that are lethal for phagocytic white blood cells
Hemolysins
Enzymes that lyse RBC's
Direct Damage
caused by certain bacteria that release toxic waste products that interfere with the host cells metabolism (may also physically lyse a host cell)
Bi-partite A-B exotoxins
have 2 separate functional regions
-B portion is involved in binding the secreted A-B toxin complex to receptors
-A portion is the active toxin portion that must be internalized into a target cell to exert toxic effects
LPS
lipopolysaccharide
Toxin
Substance that contributes to pathogenicity
Toxigenicity
Ability to produce a toxin
Toxemia
Presence of toxin in the host's blood
Toxoid
Inactivated toxin used in a vaccine
Antitoxin
Antibodies against a specific toxin
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