S7 Infections on Surfaces

Question 1

What sort of surfaces are found on a patient?

Answer 1

• skin - epithelium, hair, nails

* mucosal surfaces - conjunctival, gastrointestinal, respiratory genitourinary

Question 2

How do people get infections from themselves?

Answer 2

• invasion
• migration
• inoculation
• haematogenous

Question 3

What are some examples of external natural surface infections?

Answer 3

• cellulitis
• pharyngitis
• conjunctivitis
• gastroenteritis
• UTI
• pneumonia

Question 4

What are some examples of internal natural surface infections?

Answer 4

• endovascular (endocarditis, vasculitis)
• septic arthritis
• osteomyelitis
• empyema

Question 5

Where can you get prosthetic surface infections?

Answer 5

• intravascular lines
• peritoneal dialysis catheters
• prosthetic joints
• cardiac valves
• pacing wires
• endovascular grafts
• ventriculo-peritoneal shunts

Question 6

What are some types of microbes that can cause prosthetic valve endocarditis?

Answer 6

• streptococci
• enterococcus
• staph aureus
• candida
• coagulate negative staphylococci

Question 7

What microorganisms can cause prosthetic joint infections?

Answer 7

• coagulate negative staphylococci

* staphylococcus aureus

Question 8

What microorganisms can cause cardiac pacing wire endocarditis?

Answer 8

• coagulate negative staphylococci

* staphylococcus aureus

Question 9

What is the process of pathogenesis of infections at surfaces?

Answer 9

1. Adherence to host cells/prosthetic surface
2. Biofilm formation
3. Invasion and multiplication
4. Host response - pyogenic (neutrophils) or granulomatous (lymphocytes, macrophages)

Question 10

What structure on microbes allows them to bind to surface receptors on host cell membranes?

Answer 10

Pili or fimbriae (protein strands)

Question 11

What is a biofilm?

Answer 11

When microbes join together and produce a ‘slime layer’ which acts as a protective layer against immune cells/antibodies and complement proteins

Question 12

What is quorum sensing?

Answer 12

Communication between microbes when there are enough microbes present

Question 13

What does quorum sensing control?

Answer 13

• spore formation
• biofilm formation
• virulence factor secretion

Question 14

What are the principles of quorum sensing?

Answer 14

Microbes release signalling molecules (autoinducers - AI) that bind to cell surface/cytoplasmic receptors and cause changes to gene expression (cooperative behaviours of microbes and more AI production)

Question 15

How do you diagnose infections due to microbes on surfaces?

What are the challenges?

Answer 15

• blood cultures
• tissue/prosthetic material ultrasound and culture

Adherent organisms and small colony variants (not very virulent but are persistent/low metabolic state

Question 16

What is the treatment for infections caused by microbes on surfaces?

What are the challenges?

Answer 16

• antibacterials
• remove the prosthetic material
• surgery - cute out infected material

Poor antibacterial penetration into biofilm, low metabolic activity of biofilm microorganisms, complications of surgery

Question 17

How can you prevent infections occurring on surfaces?

Answer 17

Natural surfaces

• maintain the surface integrity
• prevent bacterial surface colonisation
• remove colonising bacteria

Prosthetic surfaces

• prevent contamination
• inhibit surface colonisation
• remove colonising bacteria

Question 18

How do microbes cause disease - what are the steps? What are the virulence factors? What type of host cell damage can occur?

Answer 18

1. Exposure 2. Adherence 3. Invasion 4. Multiplication 5. Dissemination

• exotoxins (cytolytic, AB toxins, superantigens, enzymes)
• endotoxins
• direct
• due to host immune response