PMI02-2015 Biofilms & Polymicrobial Infections

Question 1

How do infections occur in the lungs?

Answer 1

Initial viral infection causes damage to lung tissue
Tissue damage exposes the basement membrane elements such as fibrinogen to which bacteria can adhere and infiltrate not the host
Viral neuraminidase cleaves sialic acid residue on the host cell, creating more bacterial binding sites
Bronchitis or pneumonia caused by streptococcus pneumoniae
Impaired host immune response

Question 2

What does overactivity of the immune system lead to?

Answer 2

Overproduction of inflammatory cytokines leads to infiltration of bacteria, lymphocytes, neutrophils and macrophages
This damages the alveolar architecture

Question 3

What is a frequent cause of death in the elderly due to bacterial invasion?

Answer 3

Septicaemia

Question 4

What is biofilm?

Answer 4

A matrix-enclosed population of microbes that can adhere to biotic and abiotic substrates

Question 5

What are biotic substrates?

Answer 5

Skin/ mucosal surfaces/ teeth

Question 6

What are abiotic substrates?

Answer 6

dentures, resins, urinary catheters, contact lenses

Question 7

How does biofilm form in the mouth?

Answer 7

The tooth surface is coated in a salivary ‘acquired’ pellicle which contains salivary glycoproteins and primary colonisers to adhere to

Question 8

What are the advantages of biofilms over planktonic growth?

Answer 8

Increased metabolic fitness
Increased genetic diversity
Increased stress resistance
Aerobic bacteria can lower oxygen tension providing means for anaerobic species to survive

Question 9

What is recalcitrance?

Answer 9

Reduced antibiotic penetrate into the biofilm and reduced antibiotic diffusion within the biofilm

Question 10

What is the difference between types of bacteria in healthy and diseased biofilm?

Answer 10

In healthy biofilm there are more gram-positive bacteria and in diseased states there are more gram negative anaerobes

Question 11

What can changes in the biofilm cause?

Answer 11

dysbiosis

Question 12

What is periodontitis?

Answer 12

olymicrobial infection of the subgingival crevice

Question 13

How does healthy microbiota shift to gingivitis?

Answer 13

subtle changes in composition of microbiota

Question 14

How does gingivitis progress to periodontitis?

Answer 14

stabilisation of dysbiotitc polymicrobial community

Question 15

How are diabetic foot ulcers caused?

Answer 15

Inappropriate foot care and foot injuries

Underlying conditions such as: nerve damage and chronic inflammation

Question 16

How do physical polymicrobial interactions occur?

Answer 16

Co-aggregation

Question 17

How do chemical polymicrobial interactions occur?

Answer 17

Quorum-sensing

Question 18

How do nutritional polymicrobial interactions occur?

Answer 18

co-operative behaviour

Question 19

What is coaggregation?

Answer 19

Process whereby genetically distinct bacteria attach to each other via specific molecules called adhesins

Question 20

What is denture stomatitis?

Answer 20

Arises when dentures are not cleaned adequately

Biofilm accumulates on dentures and is colonised by fungi

Question 21

What is quorum sensing?

Answer 21

The regulation of gene expression in response to fluctuations in cell population density
Microbes secrete quorum sensing molecules
When present in sufficient quantities, quorum sensing molecules induce the expression or repression of quorum- dependant genes

Question 22

How do nutritional interactions occur?

Answer 22

individual microbial species are unable to completely degrade all in the substrates in the mouth, so they cooperate to do so

Question 23

What are accessory pathogens?

Answer 23

Commensal microbes that can support of enhance the virulence of a different organism

Question 24

What is an abscess caused by?

Answer 24

Introduction of endogenous oral microbes into a normally sterile tissue

Question 25

What are ‘unculturable’ bacteria?

Answer 25

Species that do not grow by themselves in lab conditions so the removed from the site of infection cannot grow isolated