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Sem 2 Infectious Diseases > Week 5 - Medical device infections > Flashcards

Week 5 - Medical device infections Flashcards

1
Q

What is a medical device?

A

Organic or inorganic medical object designed to be implanted into a normally sterile area

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2
Q

What are some types of medical devices?

A
  • Catheters/tubes, which introduce or drain fluid
  • Stents/grafts - restore a blocked tube
    Orthopaedic
    Cardiac
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3
Q

What are two types of orthopaedic devices?

A

Fracture fixation

Joitn replacementq

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4
Q

What are two types of cardiac medical devices?

A

Electrical - pacemakers etc

Mechanical - prosthetic/heart valves etc

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5
Q

What are cochlear implants for?

A

Deafness

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6
Q

When is the most common time for a device to become infected?

A

Time of insertion - skin flora/GIT/environment

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7
Q

How could a MD become infected after insertion?

A

From contamination at insertion, or from blood-bourne organisms in bacteraemia

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8
Q

Why do MDs become infected?

A
  1. Immune evasion - decreased vascularity from disruption of putting it in. Inhibition of complement, opsonization, phagocytosis by device components
  2. Biofilm formation
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9
Q

What are the two microorganism states? Describe them

A

Planktonic - float in liquid, actively replicate and actively motile
Sessile - attached to surface/another microbe. Less metabolically active, longer dividing time and preferred state for most microbes

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10
Q

What is a biofilm?

A

A community of sessile microbes attached to a surface, or each other

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11
Q

What do the bacteria produce for a biofilm?

A

Extracellular polymeric substance (EPS) –> slime, which the organisms embed themselves into

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12
Q

WHat % of bacteria are in a biofilm?

A

99.9%

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13
Q

What are sessile microbes?

A

Bacteria fungi and protozoa

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14
Q

What are the components of EPS?

A

polysaccharide & glycoproteins

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15
Q

On which surfaces do biofilms form?

A

Organic - blood vessels & bone

Inorganic - plastic, metal, rubber and silicone

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16
Q

What is the first step of biofilm formation?

A

‘Docking”

- Microbe/surface approximation and surface conditioning are required

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17
Q

What is microbe/surface conditioning composed of?

A

Organism needs to get to surface - needs fluid flow, chemotaxis, motility, hydrophobic/electrostatic interactions, temperature and pH

18
Q

What conditions a surface for docking?

A

It’s prepared by platelets and fibronectin

19
Q

What’s teh second step of biofilm formation?

A

‘Locking’

- Firms up teh connection

20
Q

What performs ‘locking’?

A

On the surface - toxin receptors and polysaccharides
The microbe - has pili, and fimbriae and produces things on it’s surface called microbial surface components recognising adhesion matrix molecules - MSCRAMMS

21
Q

What are MSCRAMMS and what do they do?

A

They mediate the initial attachment of bacteria to a surface
Critical step
usually bind to fibrinogen - also fibronectin and antibodies aka protein A, clumping factor A

22
Q

What is the third step of biofilm formation?

A

Maturation -
Planktonic microbes adhere to sessile ones. The organic/inorganic substances of the environment also adhere
Microbes then start secreting extracellular products to protect themselves

23
Q

Describe staphylococcus epidermis biofilm process

A

Staph sits to surface

  • Forms polysaccharide
  • Other bugs stick to it
  • Critical concentration of bugs allows them to secrete glycocalyx, which protects them
24
Q

Describe pseudomonas aeruginosa biofilm process

A
  1. Sticks to surface - uses flagella
  2. Migrates across surface and uses pili to aggregate community
  3. Produces exopolysaccharide
25
Q

Describe biofilm structure

A

73-98% water content
Has a coral reef like structure - water channels etc
It’s fraible at the edges

26
Q

What can penetrate into the biofilm?

A

There’s free diffusion of low molecular weight compounds - nutrients and toxins
But
Larger molecules like proteins can’t get through

27
Q

What limits size of biofilm?

A

Nutrient availability and efficiency of waste removal

28
Q

Which of the first few biofilm stages are reversible?

A

Docking

Locking is irreversible

29
Q

What’s the function of a biofilm?

A

Physical barrier to things like antibiotics
Allows attachment and division of labour - once in there they can stop producing their toxins/metabolic functions etc, but still doing ESP

30
Q

What is advantageous about the biofilm for avoiding antibiotics?

A

It’s hard to kill bugs that aren’t metabolically active - and once they’re in there, they switch off most metabolic functions

31
Q

How does virulence of bugs increase once in a biofilm?

A

They can exchange genes/virulence factors

32
Q

When does a biofilm cause systemic problems?

A

When it gets so big that it breaks apart and bacteria can spread to other areas of the body

33
Q

What is Quorum?

A

The minimum number of members of a body necessary to conduct business of that group

34
Q

What is Quorum sensing?

A

A population-dependent gene expression mechanism in some bugs

35
Q

How does Quorum sensing occur?

A

Bacteria produce small signal molecules, different between Gram pos and neg. They can sense how many other organisms by concentration of the signal

36
Q

What activities are regulated by quorum sensing?

A
  • Extracellular products i.e. toxins
  • Replication
  • Bioluminescence
37
Q

What activities are regulated by quorum sensing?

A
  • Extracellular products i.e. toxins
  • Replication
  • Bioluminescence
38
Q

In which step of biofilm formation is quorum important?

A

Step 2 - a quorum of bacteria is reached

39
Q

In which step of biofilm formation is quorum important?

A

Step 2 - a quorum of bacteria is reached

40
Q

Which step of biofilm formation is REGULATED by quorum sensing?

A

Step 3 - exopolysaccharide production

Sem 2 Infectious Diseases (3 decks)

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