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MICB 308 > Finals: Midterm 1 Content > Flashcards

Finals: Midterm 1 Content Flashcards

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1
Q

pathogen

A
  • a microbe that is capable of causing host damage
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2
Q

pathogenicity

A
  • the ability to produce disease
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3
Q

virulence (2)

A
  • degree of pathogenicity
  • only expressed in a susceptible host
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4
Q

gram negative bacteria (2)

A
  • thin peptidoglycan cell wall, surrounded by outer membrane containing lipopolysaccharide
  • double membrane
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5
Q

gram positive bacteria (2)

A
  • lack an outer membrane
  • surrounded by thick peptidoglycan cell wall
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6
Q

Koch’s Postulate: First Postulate

A
  • the microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms
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7
Q

Koch’s Postulates: Second Postulate

A
  • the microorganism must be isolated from a diseased organism and grown in pure culture
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8
Q

Koch’s Postulate: Third Postulate

A
  • the cultured microorganism should cause disease when introduced into a healthy host
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9
Q

Koch’s Postulates: Fourth Postulate

A
  • microorganism must be re-isolated from the inoculated diseased experimental host and identified as being identical to the specific causative agent
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10
Q

Challenges to Koch’s Postulates: First (3)

A
  • host susceptibility varies in human and animal populations due to a variety of factors
  • opportunistic bacteria can be found in healthy hosts too
  • may be difficult to isolate bacteria from certain areas, such as brain and bones
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11
Q

Challenges to Koch’s Postulates: Second Postulate (2)

A
  • not all bacteria can be cultured in pure form
  • many bacteria undergo genetic and phenotypic changes in culture environments
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12
Q

Challenges to Koch’s Postulates: Third Postulate (2)

A
  • not all bacterial species are equally virulent
  • closely related bacterial strains can be very different
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13
Q

Challenges to Koch’s Postulates: Fourth Postulate

A
  • re-inoculation of a host may not be possible or ethical
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14
Q

Modern Approaches to Satisfy Koch’s Postulates (4)

A
  • PCR
  • immunohistochemistry and immunofluorescence
  • ELISA
  • eliminate the pathogen and prevent/cure the disease
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15
Q

Modern Approaches to Satisfy Koch’s Postulates: PCR

A
  • PCR and 16S sequencing can be used to amplify and detect bacteria during culturing
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16
Q

Modern Approaches to Satisfy Koch’s Postulates: PCR/16S Sequencing steps (2)

A
  • 16S RNA primers are designed to detect conserved regions, with unique regions in-between that act as barcodes to identify the bacteria
  • PCR is done to amplify the bacterial nucleic acid for detection
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17
Q

Modern Approaches to Satisfy Koch’s Postulates: Immunohistochemistry (2)

A
  • microscopic images of immunohistochemical staining can be used to visualize the pathogen in the tissue directly
  • uses of antibodies against the bacteria with attached reporter enzymes
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18
Q

Modern Approaches to Satisfy Koch’s Postulates: Immunofluorescence (2)

A
  • micrographs of cells with fluorescently labelled antibodies against cell markers and bacterial
  • cells infected with bacteria will exhibit colocalization of fluorescent markers, while healthy cells will not
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19
Q

Modern Approaches to Satisfy Koch’s Postulates: ELISA (2)

A
  • use of fluorescently labelled antibodies against bacteria to detect pathogens in infection site without culturing
  • Western Blot/SDS-PAGE can be used subsequently
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20
Q

ELISA methods (3)

A
  • direct ELISA
  • indirect ELISA
  • capture/sandwich ELISA
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21
Q

Modern Approaches to Satisfy Koch’s Postulates: Eliminate the Pathogen and Prevent/Cure the Disease; Why didn’t Koch try this?

A
  • antibiotics did not exist at the time, so treatment was a lot more complicated and time-consuming
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22
Q

virulence factors

A
  • bacterial product or strategy that contributes to the ability of the bacterium to survive in the host/cause infection
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23
Q

Molecular Version of Koch’s Postulates: First Postulate

A
  • gene for virulence should be present in the strain of bacteria that cause disease and absent in avirulent strains
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24
Q

Molecular Version of Koch’s Postulates: Second Postulate

A
  • (i) knocking out or disruption the gene should reduce virulence, and (ii) introduction of the cloned gene into an avirulent strain should render the avirulent strain virulent
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25
Molecular Version of Koch's Postulates: Third Postulate
- expression of the gene should be demonstrated in human or a relevant model
26
Molecular Version of Koch's Postulates: Fourth Postulate
- antibodies or a cell-mediated immune response to a virulence factor should be protective
27
what must a pathogenic microbe do to survive in a host and establish infection (5)
- attach to host cells for colonization - evade host's innate and adaptive immune defenses and persist - obtain iron and other nutrients needed to multiply - disseminate or spread within a host and to other hosts - produce symptoms of disease (to be considered pathogenic)
28
what is adherence mediated by (2)
- bacterial appendages or surface structures - interactions can occur directly or indirectly
29
adherence: direct interactions
- "adhesin" on bacterium binds directly to a specific receptor
30
adherence: indirect interactions (2)
- adhesin binding first to the protein in the extracellular matrix (ECM) - then, the ECM proteins binds to specific receptors on the host cell, acting as a bridge
31
types of adhesins (2)
- fimbrial adhesins - afimbrial adhesins
32
fimbrial adhesins (3)
- fimbriae or pili - several types that form polymers - Pap pilus is heavily characterized and studied
33
afimbrial adhesins (2)
- several types - a single protein
34
why do bacteria use long fragile structures to bind to host cells (3)
- outreach - protection and survivability of core bacterial body from host immune system - bacterial surface and host cell are negative; allows for connection despite repulsive forces
35
can bacterium have multiple adhesins
- yes, they can be expressed all at once or sequentially during infection at different stages of pathogenesis
36
are all adhesins virulence factors (2)
- as bacteria can have multiple adhesins, it is difficult to prove necessity of any one adhesin - not all adhesins are virulence factors
37
host receptors for adhesins (4)
- often carbohydrate-based - glycolipids or glycoproteins - often integrins - receptors determine the tropism of the disease
38
tropism
- tissue specificity
39
pathogen invasion (3)
- pathogens can enter and survive in host cells - allows them to breach host epithelial barrier - provides them with protected niche for replication and persistence
40
pathogen mechanism of invasion (2)
- can actively direct their entry into host cells - usually done by a protein called "invasin"
41
invasins (2)
- activate a receptor - leads to a signaling event that enables uptake through cytoskeletal rearrangements
42
mechanisms of particle uptake into cells (2)
- zippers - triggers
43
mechanisms of particle update into cells: zippers (3)
- sequential engagement of phagocytic membrane with particle surface - pseudopod advances no further than receptor-ligand interaction permits - partial engulfment where receptor-ligand interactions are
44
mechanisms of particle update into cells: triggers (2)
- all-or-nothing effect - complete phagocytosis
45
zipper uptake steps (4)
1. initial contact (adherence) 2. receptor clustering 3. phagocytic cup formation involving actin polymerization and membrane extension 4. closure of phagocytic cup and retraction involving actin depolymerization
46
what does trigger uptake involve (3)
- mechanism similar to micropinocytosis - macropinosomes - surface ruffling
47
trigger uptake: mechanism similar to micropinocytosis
- a form of endocytosis that is accompanies by cell surface ruffling
48
trigger uptake: macropinosomes
- large vesicles that serve as a route for cells to take up macromolecules non-selectively
49
trigger uptake: membrane ruffling
- ruffles fall back onto bacteria randomly and this leads to formation of large endosomes, which eventually become smaller
50
trigger: distinct steps (3)
1. filopode formation: membrane ruffles 2. lamellipode formation: membrane ruffles filled with actin support through polymerization 3. formation of phagocytic cup made of actin or through adherence
51
zipper vs trigger (2)
- zipper results in localized contact-dependent receptor-medicated particle engulfment - trigger results in generalized engulfment event that could include neighbouring particles
52
anti-phagocytosis (2)
- some bacteria actively inhibit their uptake - secrete protein YopH through T3SS
53
can one pathogen exhibit both zipper and trigger mediated invasion
- yes, for instance, salmonella can invade host cell using different routes and mechanisms
54
phagocytosis: what is involved in uptake (2)
- microfilament rearrangements - lead to formation of a phagosome membrane
55
what does phagocytosis activate
- activation of respiratory/oxidative burst
56
normal endocytic events (4)
- early endosome - late endosome - fusion with lysosome to create the phagolysosome - destruction of the bacteria
57
Rabs
- small GTPases
58
Rab5
- early endosome marker
59
Rab7
- late endosome marker
60
LAMP1 (2)
- lysosomal associated membrane protein - phagolysosome fusion marker
61
what tools can we use to see where the phagosome is located in the pathway (3)
- western blot - IH - IF
62
bacterial phagosome survival mechanisms (4)
- failure to trigger oxidative burst by inhibiting phagosome acidification - inhibit/stall the fusion of the phagosome with the lysosome - survival within the phagolysosome - escape from the phagosome
63
autophagy (2)
- induced when cell undergoes starvation - mechanism for recycling proteins

MICB 308 (22 decks)

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