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Medical Microbiology > 1 Bacterial pathogenesis > Flashcards

1 Bacterial pathogenesis Flashcards

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Biology 101 flashcards USMLE® Step 1 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
Q

CA-MRSA resistance

A

usually not multiple resistant, but now evidence that some SCCmec Type V strains are resistant to non - b-lactams

26
Q

those at risk to CA-MRSA

A

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
Q

example of attachment to host cells

A

fibronectin binding proteins

28
Q

evasion of host immune system examples

A

Protein A

Chemotaxis inhibitory protein

29
Q

invasion and spread - exotoxins

A

alpha toxin

panton-valentine leukicidin

30
Q

Conditioning films

A

biomaterials are implanted into tissue, the very quickly become coated with host ECM proteins e.g fibrinogen, fibronectin

31
Q

Examples of S. aureus adhesin

A

FnbA/B - Fibronectin binding proteins

Cna - Collagen binding protein

32
Q

what is MSCRAMMS

A

Microbial Surface Components Recognising Adhesive Matrix Molecules

33
Q

other S. aureus adhesins

A

IsdA
Eap
Emp

34
Q

IsdA adhesin

A

iron regulated surface determinant A

35
Q

what does IsdA do

A
  • Broad spectrum adhesin
  • Binds to fibronectin and fibrinogen
  • Expression is iron regulated
36
Q

Eap adhesin

A

Extracellular Adherance protein

37
Q

what does Eap do

A
  • Broad spectrum adhesin
  • Binds to fibronectin, fibrinogen and vitronectin and promotes internalisation of S. aureus into epithelial cells
  • Expression is iron regulated
38
Q

Emp adhesin

A

Extracellular matrix protein binding protein

39
Q

what does Emp do

A
  • Broad spectrum adhesin

- Expression is iron regulated

40
Q

alpha hemolysin (hla)

A

is a cytotoxic exotoxin – help to lyse red blood cells to get iron, to use for self

41
Q

how many hemolysins does S. aureus have

A

3

42
Q

what does alpha hemolysin/toxin do

A

Membrane depolarisation – form holes in RBC

43
Q

what does PVL cause

A

These strains caused serious skin and soft tissue infections and pneumonia – pneumonia rapidly fatal

44
Q

how is PVL transferred

A

Bacteriophage involved in transfer - Phage transferred

45
Q

PVL effect on humans

A

PVL is toxic for human polymorphs – causes WBC lysis, forming holes in membrane

46
Q

Why do bacteria regulate virulence factors

A
  • 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
Q

How are virulence factors regulated?

A

Regulate at different levels

  • control transcription rate
  • control mRNA stability
  • control translation rate
  • control of protein stability
48
Q

how can virulence be altered

A

Bacteria can alter virulence gene expression in response to a signal
Signal may be environmental are internal

49
Q

External signal examples

A

Usually through receptor proteins on cell membrane
Nutrient limitation
pH
heat

50
Q

what does quorum sensing control

A

virulence factor production by S. aureus

51
Q

Why will bacteria make different decisions

A

depending on what regulators they have

52
Q

why can S.aureus cause a variety of infections

A

vast number of virulence factors

53
Q

what affects virulence gene expression

A

Environmental factors affect virulence gene expression and allow adaptation to niches within the host

54
Q

what must be tightly regulated in virulence factors

A

temporal expression

Medical Microbiology (13 decks)

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