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Mechanisms of pathogenicity
Mechanisms of pathogenicity
22
Microbiology
Undergraduate 2
12/06/2012

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Term
Parenteral
Definition
direct deposition beneath skin
bites, cuts, biological vectors, injections
Term
ID50
Definition
number entering that results in 50% probability of infection and disease in test subjects
Term
LD50
Definition
lethal dose for 50% of sample population

Usually much greater than the ID50
Term
Adherence
Definition
initial attachment to host cells is a requirement for infection by most pathogens
Attachment is usually specific for host and tissue/cell type

can result in biofilms
Term
adhesin
Definition
molecule on surface of microbe that binds to a specific molecule on surface of the host
Usually a protein
Basis for host range and specificity of some pathogens
Term
steps of infection
Definition
Adherence
Penetrance
Toxins
Term
M protein
Definition
Special cell wall component
of Streptococcus pyogenes
Adherence to epithelial cells to avoid phagocytosis
Term
Mycolic acid
Definition
Waxy lipid that helps mycobacterium resist digestion after phagocytosis.

this can help them reproduce inside of of the phagocyte.
Term
Invasins
Definition
proteins that promote entry into host cells
Term
Coagulases
Definition
promote blood clotting
Wall off infection site from host defenses
Some Streptococci
Term
Kinases
Definition
dissolve clots
Break out of confinement
Staphylokinase and streptokinase
Term
Hyaluronidase and Collagenase
Definition
break cell-cell connections and destroy tissue integrity
Allow penetration of epithelial layers.
Some streptococci and clostridia
Term
IgA proteases
Definition
destroy antibodies
Neisseria gonorrhoeae
Term
Antigenic Variation
Definition
high frequency of structural changes in molecules recognized by immune system
High mutation / recombination frequency
Term
exotoxins
Definition
proteins secreted from the bacterial cell
Some very harmful in small amounts (low LD50)
antigenic: vaccines developed against some
Term
endotoxin
Definition
Significant role in virulence of some gram negative pathogens.
Significant in opportunistic infections by gram negative bacteria.
Danger associated with perforation of large intestine or ruptured appendix.
Large numbers of gram negative bacteria in normal microflora of large intestine.
Term
A-B Toxins
Definition
exotoxin
B subunit: binds to specific target molecule on host cell surface and mediates entry into cytoplasm
A subunit: toxic effect on cell
Term
Membrane Disrupting Toxins
Definition
(type II) exotoxin

may be targeted to specific call types
Term
Superantigens
Definition
type I exotoxin

stimulate an intense immune response that damages host tissues
S. aureus
enterotoxin responsible for staph food poisoning
toxin responsible for toxic shock syndrome
Term
features that toxin names relate to
Definition
tissue affected
bacteria that secretes it
effect
Term
Lipid A component of LPS molecules
Definition
Low toxicity: high LD50
non-antigenic: no immunity to endotoxin
heat-stable: not easily inactivated by high temperature
non-specific: effects can be caused by any gram negative bacteria in blood or tissue fluids
can be released if bacterial cell lysis occurs
Term
endotoxin mechanism
Definition
stimulates abnormally large release of cytokines from macrophages and some leukocytes.
Fever
Shock: vasodilation and increased blood vessel permeability causes drop in blood pressure
called septic shock if due to endotoxin
Abnormal clot formation blocks some vessels
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