Pathogenicity Flashcards

1
Q

what are virulence factors?

A

bacteria have them and they influence the ability to cause infectious disease

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2
Q

what are the two factors of virulence factors?

A

factors that promote bacterial colonisation of host

that damage the host e.g. exotoxins and endotoxins

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3
Q

6 points that virulence factors have which promote bacterial colonisation ;

A
adhere to host cells and resist physical removal
invade host cells
contact host cells
resist phagocytosis
evade immune defences
compete for iron and other nutrients
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4
Q

name 3 ways in which the body defends against adhering bacteria

A

constant shedding of surface epethelial cells
removal of bacteria via coughing, sneezing etc
bacteria; removal by bodily fluids

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5
Q

what are the 3 mechanisms evolved by bacteria to avoid removal

A

pili
adhesions
capsules

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6
Q

what are pili?

A

a mechanism of adhesion

enables adhere to receptors on host cell= colonisation

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7
Q

what is the structure of pili?

A

thin protein tubes from cytoplasmic membrane and are found in all gram - bacteria
has a pilus

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8
Q

what is the structure of the pilus

A

shaft composed of a protein called pilim and at shaft is the adhesive tip structure - a protein celled lectin is present

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9
Q

what is lectin

A

protein found on end shaft of pilum and binds to specific glycoprotein or plycopolipid receptors on host cell

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10
Q

what are adhesion proteins

A

found in cell wall of bacteria
bind to specific receptor molecules on host cell
allow bacterium to adhere to cell and resist removal

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11
Q

what are capsules

A

produce a capsular polysaccharide matrix to form a biofilm on host tissue

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12
Q

what is a biofilm layer

A

found in capsules and consists of layers of bacteria adhering to host cells embedded in capsular mass

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13
Q

what protein allows invasion of host cells

A

invasin

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14
Q

what are invasins

A

proteins found in cell wall of bacteria -allow penetration

activate host cells cytoskeltal machinery leading to phagocytosis

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15
Q

3 ways bacteria benefit from being inside host cell

A

access to nutrient
protected from complement, antibodies etc
multiplies = disease

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16
Q

which bacteria colonise bladder and intestines and why

A

motile ones
with use of flagella to move
increases chances of reaching mucous for adhesion

17
Q

2 points about capsules and how they resist phagocytic engulfment

A

capsules enable organisms to resist this

capsules interfere with bodys complement pathway

18
Q

describe capsules and C3b

A

capsules can cover opsonin C3b bound to bacterial wall so that it cant bind to the C3b receptors on surface of phagocytes

19
Q

4 ways in which bacteria resist phagocytic destruction

A

prevent acidification pf phagosome needed for effective killing of microbes using lysosomal enzymes
kill phagocytes by producing an exotoxin which damages the cytoplasmic membrane
are more resistant to toxic forms of oxygen and defensins
block vesicular transport machinery that enables phagosome to fuse tthe lysosome

20
Q

4 ways bacteria can avoid immune defenses

A

change the adhesive tips
vary surface proteins so antibodies ‘dont fit’
have capsules made of acids present within host
produce protein A and protein g

21
Q

describe protein a and g

A

both bind to Fc portion of antibodies that normally bind to Fc receptors on phagocytes
bacterium is then coated with protective coat of antibodies

22
Q

what makes a bacterium pathogenic?

A

competition with host tissue and flora for limited nutrients

23
Q

what are AB toxins

A

consist of two parts - active a component and binding b component

24
Q

what is the b component of exotoxins

A

binds to receptor on surface of host cell

25
how does a component of exotoxins work
after b binds to host cell receptor a enters host cell by passing membrane- damage may be caused by adp-ribosylation of target host cell
26
what does the a component of AB toxins catalyse
ADP-ribosylation of host cell target proteins
27
how does NAD inactivate proteins
cleaved into ADPR which is covalently attached to host cell target protein causing inactivation
28
what is diptheria
common and leading cause of death in 1920s | immunisations carried out
29
what causes diptheria
produced by corynebacterium diptheriae
30
how doe diptheria cause disease
toxin interferes with host cell protein synthesis by catalysing the ADP ribosylation of host elongation factor 2(ef-2) necessary in order to tRNA to insert new amino acids into growing protein chain = cell death
31
what causes tetanus
produced by non-ribosylating bacterium
32
how does tetanus cause disease
neurotoxin binds to inhibitoru interneurons and blocks release of inhibitory molecules- cause contracted muscles to relax
33
how do inhibitory molecules allow muscles to relax
stop excitatory neurons from releasing acetylcholine
34
2 virulence factors that damage host
ability to produce harmful toxins | ability to produce cell wall components that bind host cells causing synthesis and secrete inflammatory cytokines
35
two points about Gram- cell walls
LPS (endotoxin) in outer membrane | it is because LPS is so immunogenic that it is toxis
36
two points about gram + cell walls
teichoic acid and peptidoglycan fragments
37
what are techoic acid composed of
polymers of glycerol, phiphates and sugar alcohol ribitol
38
2 harmful effects of bacterial cell wall components
minor infectin , few bacteria present | severe systemic infection