Infections on Surfaces

Question 1

What is a surface?

Answer 1

Interface between a liquid solid or gas

Question 2

What 5 things does a bacteria have to do in order to cause an infection

Answer 2

Exposure
Adherence 
Invasion
Multiplication
Dissemination

Question 3

What might cause a blood culture to have a false positive?

Answer 3

Microorganisms that are on the skin

Question 4

Name two viruses that can cause skin infections

Answer 4

Herpes simplex

Papilloma - warts

Question 5

How does cdiff cause a problem?

Answer 5

Invasion causes replacement of multiforal culture in bowel and becomes almost singularly occupying

Question 6

What has helicobacter pylori got to do with cancer?

Answer 6

Predisposes to increased gastric reflux, barretts oesophagus and risk of cancer

Question 7

Which 4 ways can people get infected?

Answer 7

Invasion - e.g. from a person - strep throat
Migration - e.g. from normal commensal E coli from bowel to urinary tract
Inoculation - e.g. put there - prosthetic joint
Haematogenous - e.g. via blood - strep viridian’s endocarditis

Question 8

What are natural surface infections divided into? Give examples

Answer 8

Internal - endocarditis, osteomyelitis, septic arthritis

External - cellulitis, pharyngitis, UTI, pneumonia

Question 9

Where might you see a prosthetic surface infection?

Answer 9

Cardiac valves 
Intravascular lines 
Cardiac pacing wires 
Prosthetic joints
Ventriculo-peritoneal shunts

Question 10

What is a Ventriculo-peritoneal shunts

Answer 10

Device that relieves pressure in brain

Question 11

What is the likely cause of endocarditis >1 year after valve replacement or with native valve?

Answer 11

Strep viridians
Staph aureus
Candida

Question 12

What is the likely cause of endocarditis <1 year post op prosthetic valve?

Answer 12

Staph epidermis

coagulase negative staph

Question 13

What is the most common cause of prosthetic joint infections?

Answer 13

Staph epidermis

Staph aureus

Question 14

Which is a common coagulase positive staph compared to a common coagulase negative staph

Answer 14

Positive - Aureus

Negative - Epidermis

Question 15

Difference between Empyema and Abscess?

Answer 15

Empyema is pus in an existing natural cavity e.g. pleura

Abscess is pus in a new cavity

Question 16

What kind of host responses might you have to infections e.g. on prosthetic surface (2)?

Answer 16

Pus

Granulomas (fibroblasts, lymphocytes, macrophages) leading to nodular inflammatory lesions

Question 17

What structures on bacteria help them adhere to host cell?

Answer 17

Pili

Fimbrae

Question 18

Why are biofilms resistant to antibiotics?

Answer 18

Low metabolic activity

Antibiotics most effective on metabolising organisms

Question 19

How do biofilms form? How do they communicate? What does a biofilm do?

Answer 19

Bacterial cells aggregate and adhere - secrete slime ECM matrix. Adhere to surface (first reversibly then irreversibly). Grow by multiplying and recruitment
Resist phagocytosis and antibiotics
Communication by quorum sensing

Question 20

How is biofilm behaviour controlled?

Answer 20

Quorum sensing

Question 21

What does quorum sensing control?

Answer 21

Sporulation
Biofilm formation
Virulence factor secretion

Question 22

What is a spore?

Answer 22

Structure produced by bacteria in environment change e.g. starvation. Helps with survival of bacteria as can withstand heat etc and is dormant - contains bacterial DNA

Question 23

What are the three principles of quorum sensing?

Answer 23

Signalling molecules - autoinducers that coordinate gene expression

Cell surface cytoplasmic receptors

Gene expression –> cooperative behaviours and more AI production

Question 24

How do you manage a patient with a bacterial infection that has a biofilm? What are the problems with each of these?

Answer 24

Antibacterials - biofilms resistant
Resect infected tissue
Remove prosthetics - dangers of surgery