Micro 3- pathogenesis Flashcards
pathogenicity
the ability to cause disease
virulence
the degree of pathogenicity
portals of entry
-mucous membranes
-skin
-parenteral route- deposited directly into tissues when barriers are penetrated
(most pathogens have a preferred portal of entry)
ID50
infectious dose for 50% of a sample population
-measures virulence of a microbe
LD50
lethal dose for 50% of a sample population
-measures potency of a toxin
almost all pathogens attach to host tissues in a process called
adherence (adhesion)
adhesins (ligands) on the pathogen do what
they bind to receptors on the host cells
- glycocalyx
- fimbriae
microbes form
biofilms
which allows for adherence of one microbe to the next
list of how pathogens penetrate host defenses
- capsules
- enzymes
- cell wall components
- antigenic variation
- penetration into host cell cytoskeleton
how pathogens penetrate host defenses:
capsules
- glycocalyx around the cell wall
- impair phagocytosis
ex: streptococcus pneumoniae- pnemonia, haemophilus influenzae- pneumonia and meningitis, bacillus anthracis-anthrax, yersinia pestis- plague
how pathogens penetrate host defenses:
enzymes -list
- coagulases
- kinases
- hyaluronidase
- collagenase
- IgA proteases
enzyme:
coagulases
coagulate fibrinogen
-form “wall” blood clot, fibrinogen precursors for blood clot
enzyme:
kinases
digest fibrin clots
(fibrin -> fibrinogen), from host mechanism
enzyme:
hyaluronidase
digest polysaccharides that hold cells together
enzyme:
collagenase
breaks down collagen
enzyme:
IgA proteases
destroy IgA antibodies
how pathogens penetrate host defenses:
cell wall components:
M protein
resists phagocytosis
-streptococcus pyogenes
how pathogens penetrate host defenses:
cell wall components:
Opa
protein allows attachment to host cells
-neisseria honorrhoeae
how pathogens penetrate host defenses:
cell wall components:
Waxy lipid
(mycelia acid) resists digestion
-mycobacterium tuberculosis
how pathogens penetrate host defenses:
antigenic variation
pathogens alter their surface antigens (and antibodies are rendered ineffective)
how pathogens penetrate host defenses:
penetration into host cell cytoskeleton
using invasins or using actin to move from one cell to the next
e.g. shigella and listeria
invasins
surface proteins produced by bacteria that rearrange tin filamentous of the cytoskeleton (membrane ruffling)
how can pathogens damage the host?
- using host’s nutrients (siderophores)
- direct damage
- production of toxins
damage to host:
using host’s nutrients: siderophores
- iron is required for most pathogenic bacteria
- siderophores are proteins secreted by pathogens that bind iron more tightly than host cells (ex: enterobactin)
toxins are
poisonous substances produced by microorganisms
-produce fever, cardiovascular problems, diarrhea, and shock
toxigenicity is
the ability of a microorganism to produce a toxin
toxemia
presence of toxin in the host’s blood
intoxications
presence of toxin without microbial growth
what are exotoxins?
proteins produced and secreted by bacteria
- soluble in bodily fluids, destroy host cells and inhibit metabolic functions
- gram positive
antitoxins
antibodies against specific exotoxins
toxoids
inactivated exotoxins used in vaccines
list of types of exotoxins
- AB toxins
- membrane disrupting toxins
- superantigens
AB toxins
contain an enzyme component (A part) and a binding component (B part)
example: diphtheria toxin
what do membrane disrupting toxins do? 3 types?
they lyse host cells by disrupting plasma membrane
- leukocidins
- hemolysins
- streptolysins
leukocidins
membrane- disrupting toxins
kill phagocytic leukocytes
hemolysins
membrane-disrupting toxins
kill erythrocytes by forming protein channels
streptolysins
membrane- disrupting toxins
hemolysins produced by streptococci
superantigens
cause an intense immune response due to the release of cytokines from host cells (T cells)
-cause symptoms of fever, nausea, vomiting, diarrhea, shock, and death
what are genotoxins?
they are toxins that damage DNA (causing mutations, disrupting cell division, and leading to cancer)
what are endotoxins and where do they come from
they are the lipid A portion of lipopolysaccharides (LPS) of gram negative bacteria that are released during bacterial multiplication and when gram negative bacteria die
how do endotoxins work?
they stimulate macrophages to release cytokines and cause disseminated intravascular coagulation -> blood clotting in capillaries formed - decreased blood supply, can cause damage to cells and tissues
exotoxins vs. endotoxins:
chemistry
exotoxins- proteins (usually with 2 parts- A and B)
endotoxins- lipid protein, lipid A of outer membrane LPS
exotoxins vs. endotoxins:
toxicity (ability to cause disease)
exotoxins- high
endotoxins- low
exotoxins vs. endotoxins:
bacterial source
exotoxins- mostly gram +
endotoxins- mostly gram -
what is lysogenic conversion
changes characteristics of a microbe due to incorporation of a bacteriophage
examples of bacteriophage genes:
diptheria toxin, botulinum neurotoxin and capsule produced by streptococcal pneumoniae
