Week 5 - Medical device infections Flashcards
What is a medical device?
Organic or inorganic medical object designed to be implanted into a normally sterile area
What are some types of medical devices?
- Catheters/tubes, which introduce or drain fluid
- Stents/grafts - restore a blocked tube
Orthopaedic
Cardiac
What are two types of orthopaedic devices?
Fracture fixation
Joitn replacementq
What are two types of cardiac medical devices?
Electrical - pacemakers etc
Mechanical - prosthetic/heart valves etc
What are cochlear implants for?
Deafness
When is the most common time for a device to become infected?
Time of insertion - skin flora/GIT/environment
How could a MD become infected after insertion?
From contamination at insertion, or from blood-bourne organisms in bacteraemia
Why do MDs become infected?
- Immune evasion - decreased vascularity from disruption of putting it in. Inhibition of complement, opsonization, phagocytosis by device components
- Biofilm formation
What are the two microorganism states? Describe them
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
What is a biofilm?
A community of sessile microbes attached to a surface, or each other
What do the bacteria produce for a biofilm?
Extracellular polymeric substance (EPS) –> slime, which the organisms embed themselves into
WHat % of bacteria are in a biofilm?
99.9%
What are sessile microbes?
Bacteria fungi and protozoa
What are the components of EPS?
polysaccharide & glycoproteins
On which surfaces do biofilms form?
Organic - blood vessels & bone
Inorganic - plastic, metal, rubber and silicone
What is the first step of biofilm formation?
‘Docking”
- Microbe/surface approximation and surface conditioning are required
What is microbe/surface conditioning composed of?
Organism needs to get to surface - needs fluid flow, chemotaxis, motility, hydrophobic/electrostatic interactions, temperature and pH
What conditions a surface for docking?
It’s prepared by platelets and fibronectin
What’s teh second step of biofilm formation?
‘Locking’
- Firms up teh connection
What performs ‘locking’?
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
What are MSCRAMMS and what do they do?
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
What is the third step of biofilm formation?
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
Describe staphylococcus epidermis biofilm process
Staph sits to surface
- Forms polysaccharide
- Other bugs stick to it
- Critical concentration of bugs allows them to secrete glycocalyx, which protects them
Describe pseudomonas aeruginosa biofilm process
- Sticks to surface - uses flagella
- Migrates across surface and uses pili to aggregate community
- Produces exopolysaccharide
