Session 7

Question 1

Define surface

Answer 1

The interface between a solid and liquid/gas

Question 2

What is important to remember about the surfaces of the body?

Answer 2

They are likely to have residential flora eg skin

BUT some are meant to be sterile eg heart valves

Question 3

What Gram negative fecal organisms does everyone carry from the waste down?

Answer 3

Enterobacteriase

Question 4

What Gram positive bacteria does everyone carry on their skin?

Answer 4

Coagulase negative staphylococci

Question 5

What Gram positive bacteria does 1 in 3 people carry on their skin?

Answer 5

Staphylococcus aureus

Question 6

How can microbiota (commensals) be transferred to other sites where they can cause harm?

Answer 6

Invasion
Migration
Innoculation
Haemotogenous

Question 7

How does Innoculation cause commensals to be transferred?

Answer 7

A scalpel can introduce bacteria into a new place eg Coagulative negative stapohylococcus into a prosthetic joint

Question 8

How can haemotogenous tranferring cause commensals to be harmful?

Answer 8

The blood stream can be used to deliver commensals to harmful sites. eg viridans Streptococci endocarditis

Question 9

What are some examples of prosthetic surface infections?

Answer 9

Catheters
Cardiac valves
Prosthetic joints
Endovascular grafts

Question 10

How can infections occur on prosthetic joints?

Answer 10

Low virulence bacteria bind to the joint

Question 11

How does prosthetic valve endocarditis occur?

Answer 11

Blood flow over the vales is abnormal which leads to turbulence and endothelial damage
This exposes viridan streptococci receptors
viridan streptococci binds
Vegetation occurs (Made of bacterial defences eg biofilm)
Endocarditis

Question 12

Why is it hard to manage infections with a biofilm?

Answer 12

It is very hard to penetrate the Biofilm (Made of proteins etc) to get to the bacteria making it.

Question 13

What is the process of pathogenesis of infections on surfaces?

Answer 13

Adherence
Biofilm formation
Invasion (of host tissues) and multiplication
Host respone (Pyogenic - Pus forms. Granulomatous)

Question 14

How do pili/fimbriae aid bacteria?

Answer 14

They help adhere to the memebranes

Question 15

How do bacteria excrete waste products from their biofilms?

Answer 15

There are channels that allow nutrients in and waste out (Biofilms use lots of energy)

Question 16

What is Quorum sensing?

Answer 16

A system of stimulus and response correlated to population density of bacteria. Bacteria will coordinate gene expression depending on the stimuluses around them

Question 17

What does Quorum sensing control?

Answer 17

Sporulation
Biofilm formation
Virulence factor secretion

Question 18

What are the 3 principles of Quorum sensing?

Answer 18

Signalling molecules - autoinducers
Cell surface/cytoplasmic receptors
Gene expression (cooperative behaviours and more autoinducer production)

Question 19

What are virulence factors?

Answer 19

Molecules secreted and excreted by pathogens to allow them to establish an infection in many ways. eg Endo/Exo toxins

Question 20

How can you use blood cultures to distinguish a source of infection?

Answer 20

Take a blood sample from the central line and a peripheral vein. Culture both and if the central line grows bacteria faster then it suggests the central line is the source of infection.

Question 21

How can you use flushing to see if there is a biofilm in a cannula?

Answer 21

If you flush the cannula and there is related pyrexia it suggests that the cannula has a biofilm in it

Question 22

What is the course of action for someone with an infected prosthetic joint?

Answer 22

Remove the infected prosthetic joint
Insert spacers
Place on antibiotics for around 6 weeks
Insert a new prosthetic joint

Question 23

How can you prevent bacterial infections?

Answer 23

Maintain the natural surface’s integrity eg silver coated IV lines/catheters, no pressure sores, avoid breaches in surface epithelium - healing by primary intention.
Removing colonising bacteria

Question 24

When is it hard to close a wound by primary intention?

Answer 24

If there is too much inflammation. In this case the wound needs to be protected from bacteria entering somehow