Test 3-5 (Host-Parasite) Flashcards
-- List the major microbial virulence factors and mechanisms of pathogenesis -- Understand adherence phenomena & methods for pathogen resistance to phagocytosis -- Describe the role of capsules, biofilms, toxins, superantigens, & destructive enzymes in disease -- Define the importance of exaggerated immune response in the pathogenic effect produced by various microbes in the human host -- List the normal bacterial flora found in the main body regions, and differentiate from adjac
bacterial toxins in food incubates…
over a few hours pt will have symptoms
THE TOXIN CAUSES THE PROBLEM. NOT AN INFECTION.
severe limiting vomiting and diarrhea are typical of…
staphylococcal food poisoning - no antibiotics will help…this kind will pass
toxin that causes tetanus?
clostridium tetani - produces the damaging effect on the neurological system
toxin that causes pneumonia
stroptococcus pneumoniae (capsule)
seropositive response
good immune response to infecting agent
beneficial effects
- Vitamin Synthesis (vitamin K)
- Bile Pigment Degradation
- Inhibition of Growth of
Potential Pathogens
a. Antigenic priming
b. Bacteriocin secretion
c. Low redox potential
d. Supression of adherence
NORMAL FLORA definition, locations, colonization
- Definition: indigenous microflora part of “healthy” body surfaces
- Locations: Mouth, upper respiratory tract & gut
- Colonization: Acquired at birth
Microbiome
set of unique human- associated bacteria
Lower respiratory & upper urogenital tracts: -
Sterile normally- Susceptible to microbial “invasion” from adjacent sites
incubation time
between time of first contact and onset of symptoms
direct exposure
skin to skin
aerosol exposure
respiratory droplet
fomite exposure
towel, doorknob
Virulence factors:
any mechanisms used to avoid host’s defenses (term sometimes used to describe any trait that increases virulence)
Invasion
- Some microbes cross mucous membranes or other barriers to reach normally sterile areas
- Most destroy barrier or penetrate cells
Enteric bacteria and invasion
- synthesize “invasion protein” that promotes binding to M cells in colon
- Binding causes cells to invaginate, take in bacteria.
Bacteria invasion mechanisms
- some spread to adjacent cells (cell-to-cell)
- others move inward to the bloodstream (hematogenous spread)
adherence does what?
mediates infection. No adherence=no infection.
what is the primary mech for attachment of bacteria to tissue surfaces?
adhesin on bacteria binds receptor on host
where are adhesins usually located?
tips of pili for gram-neg bactiea
colonization of bacteria is dependent on
environmental conditions! temperature or tissue type
biofil def and function
- –Bacterial cells (usually many cells) in a sticky web of polysaccharide
- –Polysaccharide has several functions:
- Binds bacterial cells together
- Binds entire biofilm to surface
- Protects bacteria from antibiotics & host defense mechanisms
MICROBIAL SURVIVAL STRATEGIES
1) Inhibition of host immune mediators
- -IgA protease - Streptococcus pneumoniae
- -Subverts phagocytosis
- -Capsules prevent ingestion
- -Leukocidins kill PMNs and macrophages
2) Intracellular growth pattern (agent can go inside where immune system cant detect
3) Capsules - shield from microbes from immune response - may use molecular mimicry
4) Avoiding phagocytosis
5) Hiding and growing inside cells (parasites, fungi, viruses)
6) Bait and switch
Toxins: Definition
- Bacterial molecules that directly harm tissue or trigger destructive activities
- Solely responsible for production of symptoms in some bacterial diseases
- Distributed through bloodstream & able to act systemically; in some cases, bacterium need not enter body at all
exotoxin
secreted outside the cell
endotoxin
lipopolysaccharide or LPS (ONLY GRAM NEG)
B” subunit …
binds to human cellular receptor
“A” subunit…
is the active portion, poisons host cellular processes
Superantigens
- Special groups of toxins; activate T-cells
- Simultaneously bind to receptor on T-cell & MHC II receptor on another cell (no specific antigen required)
- Non-specific mechanism for activation of T-cells (i.e., can activate any T-cell)
- Example: Staphylococcal enterotoxins
