Pathogenesis of periodontal diseases

Question 1

Gram positive vs gram negative bacteria

Answer 1

Gram positive: only one membrane and a thick peptidoglycan layer which when included in the gram stain method retains the stain in side the cell causing it to appear purple
Gram negative: two membranes with a thin cell wall between the two mems creating a space called the peroiplasm. And have an outer capsule of LPS. Does not retain the stain so appears pink under light microscope

Question 2

Koch’s postulates

Answer 2

traditional view of infection. One organism –> one infection
Not seen as the case anymore

Question 3

Periodontal progression

Answer 3

Health –> gingivitis (inflammation) –> moderate periodontal disease (pocket) –> advanced periodontal disease (bone loss)

Question 4

Loe longitudinal studies

Answer 4

Gingivitis develops when plaque accumulates

Health restored when plaque removed

Question 5

Germ-free animals

Answer 5

No bacteria, no disease
Germ-free plus bacteria –> disease (but not all animals equally)
Periodontitis-causing bacteria ‘transmissable’ (disease may or may not arise)

Question 6

Layers of organisms in subgingival plaque

Answer 6

Firmly attached: deeper layer, predominantly gram+
Loosely attached: more superficial layer, gram- anaerobes and motile bacteria
Exist in close, mixed communities

Question 7

Disease progression

Answer 7

Sporadic and often site specific

Question 8

What changes a quiescent site to an active one?

Answer 8

Change in host - immune status, age, environmental factors (smoking etc)
Change in microbial challenge
-type of organisms
-number of particular organisms
-virulence of organism

Question 9

Problems with sampling subgingival plaque

Answer 9

If tooth is posterior and difficult to access

Might sample supragingival plaque

Question 10

Instruments to sample subgingival plaque

Answer 10

Use a curette or paper point

Question 11

The idea of the (oral) microbiome

Answer 11

The microbiome affects the way that you live
In our bodies we carry around 1kg mass in bacteria (mainly in digestive tract)
Profound influence on our health
-GU health (females)
-GU health > IBD
-GI food processing > obesity

Question 12

Establishing microbes in subgingival plaque

Answer 12

Methods:

1. Culture up to late 90s
2. Sequencing 16s rRNA PCR clone libraries/ hybridisation arrays
3. Mass sequencing of 16s rRNA amplicons

Question 13

Why do we use 16s rRNA sequencing to identify species?

Answer 13

16s rDNA very well conserved due to esssential function
Acts as molecular clock and species signature as evolves slowly in time
We sequence it to speciate bacteria (18s is human/ animal equivalent)

Question 14

Firmicutes & streps

Answer 14

Omnipresent in samples, not contributing to disease

Question 15

Bacteroidetes

Answer 15

Raised in disease

Anaerobic, Gram- bacilli

Question 16

Unculturables

Answer 16

~500 species present

~50% can be cultured

Question 17

Evidence for specific microbial aetiology

Answer 17

High numbers of certain bacteria cultured from diseased sites
Can cause disease in certain animal models
Have demonstrable virulence factors

Question 18

Groups of organisms in periodontitis

Answer 18

Health: S. mitis, S. oralis
Disease: P. gingivalis, Ta. forsythia

Question 19

P. gingivalis

Answer 19

Black pigmented anaerobe
Lipopolysaccharide in outer membrane
Gram negative
Secretes gingipains - virulence factors (proteases which degrade protein)
Epithelial cell invasion - immune evasion and recolonisation after debridement (hides)
Surface proteins key to human-cell interaction

Question 20

Ta. forsythia

Answer 20

Anaerobe (not black)
Gram -ve
Unusual structure
Tooth-like S- layer: responsible for aspects of adhesion (glycosylated?)
Fibronectin binding protein
Protease/ toxins
Glycosidases give it competitive advantage

Question 21

Sheffield findings Tannerella

Answer 21

Sialic acid is key nutritional source for Tannerella
Acquisition of sialic acid requires cleavage from host proteins
-inhibition with Tamiflu stops growth. New treatment?

Question 22

T. denticola

Answer 22

Small, thin spiral shaped bacterium
Few known virulence factors
Difficult to grow and work with

Question 23

Groups of organisms are more important than single pathogens

Answer 23

Diff bacteria have diff virulence factors
Combination of these factors more likely to cause disease
Qualitative mixture of pathogens determines disease progression

Question 24

Dysbiosis

Answer 24

Move from health to disease

Healthy community –> environmental factors –> disease community

Question 25

Keystone hypothesis

Answer 25

P. gingivalis has been shown to shift whole pop. from non-pathogenic to pathogenic in mouse models even if only present in low numbers
Also noticed in obesity

Question 26

Imbalance in innate immunity

Answer 26

Can –> bone loss

Question 27

Mechanisms of tissue damage

Answer 27

Bacteria:

Evasion of host defences, induction of inflammation (cytokines) –> bone resorption, soft tissue damage

Question 28

Necrotising ulcerative gingivitis

Answer 28

Tissue damage
Depression of host defences by smoking and modification of response by stress
Possibly depression of peripheral blood supply to tips of papillae
Selection of specific bacteria by host-derived nutrients
Fuso-spirochaetal complex

Question 29

Polymicrobial infections

Answer 29

Caused by interactions between 2 or more organisms leading to disease
Sum of parts and their virulence factors cause disease, not one in isolation
Interaction with host defences often key