ID: Biofilm-associated infections

Question 1

What are types of medical devices?

Answer 1

• Catheters
• Stents and grafts
• Orthopaedic
  
  • Fracture fixation.
  • Joint replacement.
• Cardiac
  
  • Electrical
  • Mechanical
• Other
  
  • Surgical clips
  • Cochlear implants
  • Intraocular lenses

Question 2

What are 3 ways medical devices become infected (at time of insertion)?

Answer 2

• Skin flora.
• Gastrointestinal flora.
• Environmental flora.

Question 3

How can medical devices become infected after insertion?

Answer 3

• Contamination at insertion.
• Blood-borne organisms (bacteraemia) e.g. prosthetic hip 1 year ago; visit to dentist, bleeding; bacteria from mouth end up swimming through body to stick to device.

Question 4

Why do medical devices become infected?

Answer 4

• Immune evasion
  
  • Decreased vascularity
  • Inhibition of complement activation, opsonisation, phagocytosis by device components.
• Biofilm formation

Question 5

What are the 2 states microorganisms exist in?

Answer 5

• Planktonic.
  
  • Floating in liquid media.
  • Actively replicate.
  • Actively motile.
• Sessile.
  
  • Attached to surface/another microbe.
  • Less metabolically active.
  • Preferred state of

SESSILE = BIOFILM.

Question 6

What is a biofilm?

Answer 6

• Community of sessile microbes attached to a surface or each other.
• Embedded in extracellular polymeric substance (slime) they produce.

Question 7

What are the 3 essential components of a biofilm?

Answer 7

1. Sessile microbes.
2. Extracellular substance.
3. Surface.

Question 8

What are the 2 most common extracellular substances?

Answer 8

• Polysaccharide.
• Glycoprotein.

Question 9

What are the 3 stages of biofilm formation? (Hint: space shuttle)

Answer 9

1. Docking.
2. Locking.
3. Maturation.

Question 10

What factors aids in “docking” during biofilm formation?

Answer 10

• Microbe/surface approximation (e.g. electrostatic interaction, pH).
• Surface conditions (e.g. platelets cover devices - enhance sticking of microbes).

Question 11

What factors aid in “locking” during biofilm formation?

Answer 11

• Surface:
  
  • toxin receptors
  • polysaccharides
• Microbe:
  
  • microbial surface components recognising adhesion matrix molecules: MSCRAMMS)
  • pili
  • fimbriae

Question 12

What do MSCRAMMS normally bind to?

Answer 12

Fibrinogen (also fibronectin, antibodies)

In Staphylococcus aureus, MSCRAMMS are made of protein A, and clumping factor A (ClfA)

Question 13

What are the main components of maturation in biofilm formation?

Answer 13

• Planktonic microbes adhere to sessile ones.
• Substances from the environoment also adhere.
• Microbes secrete extracellular products (to protect them and help mature biofilm).

Question 14

What are biofilms made of?

Answer 14

• 73-98% water.
• “Coral reef” structure
  
  • Channels and mushrooms.
• Friable at edges.
• Free diffusion of low molecular weight compounds (nutrients and toxins: proteins, antibodies can’t penetrate).

Question 15

What are the 5 stages of P. aeruginosa biofilm formation?

Answer 15

Question 16

How is biofilm formation regulated?

Answer 16

• Quorum sensing.
  
  • Population-dependent gene expression.