Infections On Surfaces

Question 1

Name some surfaces found on a patient

Answer 1

Skin: epithelium, hair, nails

Muscosal surfaces: conjunctival, GI, respiratory, genitourinary

Question 2

Name some viruses found on the skin (2)

Answer 2

Papilloma

Herpes simplex

Question 3

Name some bacteria found on the skin (4), specify whether they’re gram negative or positive

Answer 3

Gram positive: staph aureus,
Coagulate negative staphylococci
Corynebacterium

Gram negative: enterobacteriaceae

Question 4

Name some fungi that are found on the skin (2)

Answer 4

Yeasts

Dermatophytes

Question 5

Name a parasite that can be found on the skin (1)

Answer 5

Mites

Question 6

Why is it important to always clean the skin site before taking blood?

Answer 6

Because the natural fora on the skin can get into the blood culture

Question 7

Give some examples of the natural flora found in the eye?

Answer 7

Coagulate negative staphylococci, diphtheriods, saprophytic neisseria species, viridans group streptococci

Question 8

Name a bacteria that can be found in the nares (nose)

Answer 8

Staph aureus

Question 9

What can be given prior to a cardiovascular operation to prevent infections of the wound?

Answer 9

Nasal antibiotics

Question 10

What natural flora can be found in the nasopharynx?

Answer 10

Neisseria meningitidis, streptococcus pneumoniae, haemophilus influenzae

Question 11

Name some infections that you can get on the external surfaces of the body (6)

Answer 11

Cellulitis 
Pharyngitis
Conjunctivitis 
Gastroenteritis 
UTI
Pneumonia

Question 12

Name some infection that you can get on internal surfaces of the body (4)

Answer 12

Endovascular (endocarditis, vasculitis)
Septic arthritis
Osteomyelitis (bone infection)
Empyema (infection of alveoli in pleural space)

Question 13

Name some prosthetic surfaces that may offer a site for potential infections to occur?

Answer 13

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

**bacteria can be introduced at the time of the surgery and lay dormant for months whilst there is internal conflict between the host immune system.

Question 14

What bacteria is most likely to be the cause of pacemaker endocarditis?

Answer 14

Coagulative negative staphylococci

Question 15

What organism is likely to be the cause of native and prosthetic valve endocarditis >1 year post-operation? (5)

Answer 15

Viridans streptococci
Enterococcus faecalis
Staph aureus
HACEK group
Candida

Question 16

What is the organism likely to cause prosthetic valve endocarditis <1 year post-operation?

Answer 16

Coagulate negative staphylococci

Question 17

What are the two most likely organisms that will cause prosthetic limb infections? (2)

Answer 17

Coagulase negative staphylococci

Staphylococcus aureus

Question 18

What are the likely organisms that cause Cardiac pacing wire endocarditis? (2)

Answer 18

Coagulate negative staphylococci

Staphylococcus aureus

Question 19

What are the 4 stages of pathogenesis of infection at surfaces?

Answer 19

1) adherence to host cells or prosthetic surface
2) biofilm formation
3) invasion and multiplication
4) host response (pyogenic/granulomatous)

Question 20

What do bacteria have to help them adhere to surfaces?

Answer 20

Pili

Question 21

What is a biofilm?

Answer 21

A thick slim layer which can help protect bacteria against attack and host defence.

*aggregated cells can become detached, or roll or ripple along the surface and remain in their protected biofilm state

**although antimicrobial damages out cells, the biofilm community is resistant

Question 22

What is quorum sensing?

Answer 22

Quorum sensing is a system of stimuli and response correlated to population density. Quorum sensing (QS) allows bacteria to restrict the expression of specific genes to the high cell densities at which the resulting phenotypes will be most beneficial. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population.

Question 23

What does a biofilm contain?

Answer 23

Proteins, nucleic acids, polysaccharides

Question 24

What does quorum sensing control?

Answer 24

• sporulation
• biofilm formation
• virulence factor secretion

Question 25

How does quorum sensing result in more biofilm production?

Answer 25

Signalling molecules called auto-inducers (AI) are produced

These bind to cell surface/cytoplasmic receptors

This causes gene expression to be changed and more AI and biofilm is produced

Question 26

How are infections on surfaces managed?

Answer 26

Diagnosis- identify infecting organism and its antimicrobial susceptibilities

Question 27

How can you identify an infecting organism causing a surface infection?

Answer 27

Blood culture

Tissue/prosthetic material sonication and culture \\

Question 28

What are the challenges of culturing bacteria that are in a biofilm?

Answer 28

• adherence: they are sticking well to the surface and can be difficult to separate from surface
• low metabolic state: in the biofilm the bacteria are ‘at rest’ so are difficult to culture because they aren’t really growing that much

Question 29

How is an infection on a surface treated? What are the aims?

Answer 29

Aims: sterilise tissue, reduce bioburden.

• Give antibacterials
• remove prosthetic material (this can carry significant mortality risks)
• surgery (replace joint with antibiotic cement as temporary fix, then give new joint later)

Question 30

What are the challenges of treating infections on surfaces?

Answer 30

• poor antibacterial penetration into biofilm
• low metabolic activity of biofilm microorganisms
• dangers/difficulties of surgery

Question 31

How can infections on natural surfaces of the body be prevented?

Answer 31

• maintain surface integrity (eg good oral hygiene)
• prevent bacterial surface colonisation
• remove colonising bacteria

Question 32

How can you prevent infections on prosthetic surfaces within the body?

Answer 32

• prevent contamination
• inhibit surface colonisation
• remove colonising bacteria