S6) Surface Infections

Question 1

Define a surface

Answer 1

A surface is an interface between a solid and either a liquid or a gas

Question 2

In terms of the infection model for surface infections, identify and describe the two types of surfaces involved

Answer 2

• Skin: epithelium, hair, nails
• Mucosal surfaces: GI, GU, resp, conjunctival

Question 3

Identify the types of micro-organisms found on the skin and provide examples

Answer 3

• Viruses – papilloma, herpes simplex
• Bacteria – S.aureus, Coagulate negative staphylococci, Enterobacteriaceae
• Fungi – yeasts, dermatophytes
• Parasites – mites

Question 4

Identify 5 different ways people get surface infections and provide examples of each

Answer 4

• Microbiota
• Invasion e.g. Strep pyogenes in pharyngitis
• Migration e.g. E.coli in UTI
• Inoculation e.g. Coagulate negative staphylococcus in prosthetic joint infection
• Haematogenous e.**g. viridans Strep in endocarditis

Question 5

Provide some examples of external natural surface infections

Answer 5

• Cellulitis
• Pharyngitis
• Conjunctivitis
• Gastroenteritis
• UTI

Question 6

Provide some examples of internal natural surface infections

Answer 6

• Endocarditis
• Septic arthritis
• Osteomyelitis
• Empyema

Question 7

Provide 5 medical devices/procedures which could give rise to prosthetic surface infections

Answer 7

• Intravascular lines
• Peritoneal dialysis catheters
• Prosthetic joints
• Cardiac valves
• Pacing wires

Question 8

What are the causative organisms for prosthetic valve endocarditis?

Answer 8

• Prosthetic valve endocarditis > 1 year post-operation: viridans Streptococci, Staph aureus
• Prosthetic valve endocarditis < 1 year post-operation: Coagulase negative staphylococci

Question 9

What are the causative organisms for prosthetic joint infections?

Answer 9

• Coagulase negative staphylococci
• Staphylococcus aureus

Question 10

What are the causative organisms for cardiac pacing wire endocarditis?

Answer 10

• Coagulase negative staphylococci
• Staphylococcus aureus

Question 11

In 4 steps, outline the pathogenesis of surface infections

Answer 11

⇒ Adherence to host cells / prosthetic surface

⇒ Biofilm formation

⇒ Invasion and multiplication

⇒ Host response

Question 12

Identify and describe the two possible host responses in the pathogenesis of surface infections

Answer 12

• Progenitor: neutrophils → pus
• Granulomatous: fibroblasts, lymphocytes, macrophages → nodular inflammatory lesions

Question 13

Explain the process involved in biofilm formation in the pathogenesis of surface infections

Answer 13

Biofilm formation is a process whereby microorganisms irreversibly attach to and grow on a surface and produce extracellular polymers that facilitate attachment and matrix formation

Question 14

In detail, explain how micro-organisms cause disease

Answer 14

Question 15

In management of a surface infection, outline the diagnosis of it

Answer 15

Aim is to identify infecting organism and its antimicrobial susceptibilities:

• Blood cultures
• Tissue/prosthetic material sonication and culture

Question 16

In management of a surface infection, outline the treatment of it

Answer 16

Aim is to sterilise the tissue and reduce bioburden:

• Antibacterials
• Remove prosthetic material
• Surgery – resect infected material

Question 17

In management of a surface infection, outline the prevention of it

Answer 17

• Natural surfaces: maintain surface integrity, prevent bacterial surface colonisation, remove colonising bacteria
• Prosthetic surfaces: prevent contamination, inhibit surface colonisation, remove colonising bacteria