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1 Bacterial pathogenesis Flashcards

1
Q

Pathogenicity

A

capacity of a microbe to cause damage in a host

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2
Q

Virulence

A

relative capacity of a microbe to cause damage in a host (severity)

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3
Q

Virulence factor

A

molecule produced by microbe that promotes pathogenicity

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4
Q

Bacteria disease host responses

A
  1. Colonisation – adhesion, nutrient acquisition (produces lots of enzymes to acquire these)
  2. Invasion of tissues
  3. Avoidance of host defences
  4. Tissue damage
  5. Transmission
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5
Q

S. aureus gram stain

A

Gram purple – retain crystal violet due to thicker peptidoglycan layer
positive facultative anaerobe

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6
Q

S. aureus size and shape

A

Cocci, 1µm diameter

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7
Q

S. aureus resistance

A

Some strains are resistant to all known antibiotics

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8
Q

how many are carriers of S. aureus

A

part of normal microflora
20% persistent
60% intermittent

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9
Q

what type of pathogen is S. aureus

A

commensal
or
Opportunistic pathogen that can cause a wide range of diseases

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10
Q

Examples of staphylococcus diseases

A

Pimple
Impetigo
TSS

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11
Q

S. aureus transfer

A

Horizontal gene transfer can occur – e.g plasmids, transposons, pathogenicity islands, bacteriophage, SCCmec

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12
Q

S. aureus and environment

A

Organism is continually changing and adapting in response to its environment

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13
Q

Antibiotic Resistance - S. aureus

A

Staphylococcal antibiotic resistance is a major problem particularly in hospitals.
Methicillin Resistant S. aureus (MRSA)

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14
Q

what causes S. aureus resistance

A

production of a new penicillin binding protein (PBP2a) encoded on SCCmec

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15
Q

what is SCCmec

A

Staphylococcal cassette chromosome mec

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16
Q

what does SCCmec do

A

Mobile genetic (moved around by bacteriophage) element that integrates at the attB phage site of S. aureus chromosome

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17
Q

what is HA-MRSA

A

Hospital Acquired MRSA

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18
Q

why is S. aureus resistant to b-lactams antibiotics

A

“accumulation” of lactamase

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19
Q

what is the drug of choice for MRSA infection

A

Vancomycin

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20
Q

what is VISA or GISA

A

S. aureus with reduced sensitivity to vancomysin have been isolated
Called VISA or GISA strains = vancomycin/glycopeptide intermediate S. aureus

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21
Q

what is VRSA

A

vancomycin resistance has been found in a small number of S. aureus

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22
Q

CA-MRSA strains

A

strains are genetically more diverse (exposed to varying bacteria) than hospital acquired MRSA

23
Q

what is CA-MRSA associated with

A

SCCmec type IV and V elements

24
Q

what are CA-MRSA usually resistant to

A

Type IV and V SCCmec elements only usually confer resistance to b-lactams

25
CA-MRSA resistance
usually not multiple resistant, but now evidence that some SCCmec Type V strains are resistant to non - b-lactams
26
those at risk to CA-MRSA
Young – children and young adults Contact sports - skin abrasion (MMA/ Wrestling) Sharing towels and athletic equipment weakened immune systems e.g HIV/AIDS patients
27
example of attachment to host cells
fibronectin binding proteins
28
evasion of host immune system examples
Protein A | Chemotaxis inhibitory protein
29
invasion and spread - exotoxins
alpha toxin | panton-valentine leukicidin
30
Conditioning films
biomaterials are implanted into tissue, the very quickly become coated with host ECM proteins e.g fibrinogen, fibronectin
31
Examples of S. aureus adhesin
FnbA/B - Fibronectin binding proteins | Cna - Collagen binding protein
32
what is MSCRAMMS
Microbial Surface Components Recognising Adhesive Matrix Molecules
33
other S. aureus adhesins
IsdA Eap Emp
34
IsdA adhesin
iron regulated surface determinant A
35
what does IsdA do
- Broad spectrum adhesin - Binds to fibronectin and fibrinogen - Expression is iron regulated
36
Eap adhesin
Extracellular Adherance protein
37
what does Eap do
- Broad spectrum adhesin - Binds to fibronectin, fibrinogen and vitronectin and promotes internalisation of S. aureus into epithelial cells - Expression is iron regulated
38
Emp adhesin
Extracellular matrix protein binding protein
39
what does Emp do
- Broad spectrum adhesin | - Expression is iron regulated
40
alpha hemolysin (hla)
is a cytotoxic exotoxin – help to lyse red blood cells to get iron, to use for self
41
how many hemolysins does S. aureus have
3
42
what does alpha hemolysin/toxin do
Membrane depolarisation – form holes in RBC
43
what does PVL cause
These strains caused serious skin and soft tissue infections and pneumonia – pneumonia rapidly fatal
44
how is PVL transferred
Bacteriophage involved in transfer - Phage transferred
45
PVL effect on humans
PVL is toxic for human polymorphs – causes WBC lysis, forming holes in membrane
46
Why do bacteria regulate virulence factors
- High metabolic burden - Only expressed when they provide a growth or survival advantage - Allows S. aureus to adapt to different niches within the host
47
How are virulence factors regulated?
Regulate at different levels - control transcription rate - control mRNA stability - control translation rate - control of protein stability
48
how can virulence be altered
Bacteria can alter virulence gene expression in response to a signal Signal may be environmental are internal
49
External signal examples
Usually through receptor proteins on cell membrane Nutrient limitation pH heat
50
what does quorum sensing control
virulence factor production by S. aureus
51
Why will bacteria make different decisions
depending on what regulators they have
52
why can S.aureus cause a variety of infections
vast number of virulence factors
53
what affects virulence gene expression
Environmental factors affect virulence gene expression and allow adaptation to niches within the host
54
what must be tightly regulated in virulence factors
temporal expression

Medical Microbiology (13 decks)

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