Infections on Surfaces

Question 1

How is a surface defined?

Answer 1

An interface between a solid and a liquid/gas e.g skin and mucosal surfaces

Question 2

What is the microbiota?

Answer 2

commensal microorganisms carried on skin and mucosal surfaces, they can be harmful if they travel elsewhere in the body

Question 3

By what mechanisms can commensal microorganisms travel?

Answer 3

invasion e.g strep progenes pharyngitis
inoculation e.g coagulase negative staph. in joint replacement procedure
haematogenous e.g viridian’s strep endocarditis in poor oral hygiene
migration e.g. e coli in UTIs

Question 4

What kind of organisms live on the skin?

Answer 4

viruses- papilloma, herpes simplex

gram positive bacteria- staph aureus, coagulase negative staphylococcus

gram negative bacteria- enterobacteriaciae

fungi- yeast, dermatophytes

parasites- mites

Question 5

What are some natural surface infections?

Answer 5

Natural ​ surface infections

External- Cellulitis, Gastroenteritis, Pneumonia

Internal- UTI, Endocarditis, Empyema, Septic arthritis, Osteomyelitis

Question 6

What are some prosthetic surface infections?

Answer 6

Prosthetic ​

● Intravascular lines
● Prosthetic joints – coagulase negative staphylococci/ staph aureus
● Prosthetic cardiac valves – coagulase negative staphylococci/ viridians streptococci/
staph aureus (can be from patient’s skin or surgeon’s skin)
● Pacing wires - coagulase negative staphylococci/ staph aureus
● Endovascular grafts

Question 7

What are some organisms found on prosthetic cardiac valves at different times?

Answer 7

Native valve endocarditis and prosthetic valve endocarditis over 1 year post op: virdans streptococci, enterococcus faecalis, staph. aureus, HACEK group, candida

Prosthetic valve endocarditis less than 1 year post op: coagulase negative staphylococci

Question 8

Describe the pathogenesis of infections at surfaces

Answer 8

1) adherence- via pili/fimbraiea attaching to host cell (in endocarditis, damaged valve means fibronectin is exposed)
2) biofilm formation- bacteria stick to each other and they are embedded in a matrix of extracellular polymer substances (slime)) which protects against host defence. parts can also break off and go elsewhere too.

note- quorum sensing is where bacteria detect and respond to surrounding environmental conditions

3) invasion and multiplication
4) host response- pyogenic or granulomatous

Question 9

How would you manage a surface infection?

Answer 9

Diagnosis:

Blood cultures and tissue cultures from potential infection site

Treatment:

• Sterilise tissue
• Antimicrobials
• Remove prosthetic material (if possible)

Prevention:

• Prevent colonisation
• Prevent contamination
• Inhibit surface colonisation
• Remove colonies

Problems with this are penetrating into biofilm