Microbiology Of Periodontal Disease

Question 1

What anaerobes are involved in periodontal diseases?

Answer 1

Gram negative anaerobes- spirochaetes, Porphyromonas gingivalis, Tannerlla forsythia, Aggregibacter actinomycetemcomitans

Question 2

What is the definition of dental plaque?

Answer 2

Structured, resilient yellow/grey substance that adheres tenaciously to intraoral hard surfaces, including removable and fixed appliances and restorations, it is a biofilm community of microorganisms

Question 3

How does biofilm form and mature?

Answer 3

As plaque matures gram positive bacteria are gradually replaced by gram negative species. This causes the formation of gram negative filamentous forms such as fusiforms (spindle shaped bacteria) and spirochaetes (cork screw shaped bacteria) appear in the later stages of plaque maturation.

Question 4

What is dental plaque composed of?

Answer 4

80-90% water with 70% of the dry weight being made up of bacteria

Question 5

What is calculus?

Answer 5

Calcified dental plaque and is 70-80% inorganic salts (hydroxyapatite)

Question 6

What is supra-gingival plaque composed of?

Answer 6

It is 50% matrix, mostly gram positive, aerobic bacteria

Question 7

What is sub-gingival plaque composed of?

Answer 7

Contains little or not matrix, mostly gram negative rods and spirochetes, less oxygenated so favours the growth of anaerobes

Question 8

In what areas does dental plaque form quicker?

Answer 8

Lower jaw, molar areas, buccal tooth surfaces, interdental regions

Question 9

Name two out-dated periodontal disease hypotheses.

Answer 9

Specific plaque hypothesis and the non-specific hypothesis

Question 10

What does the specific plaque hypothesis of periodontal disease propose?

Answer 10

Only a few specific species out of the diverse collections of microorganisms in plaque are actively involved in disease

Question 11

What does the non-specific plaque hypothesis of periodontal disease propose?

Answer 11

The disease is considered to be of the outcome of the overall activity of the total plaque microflora

Question 12

What is the main hypothesis for the development of periodontal disease?

Answer 12

The ecological plaque hypothesis

Question 13

What does the ecological plaque hypothesis for periodontal disease propose?

Answer 13

The organisms associated with disease may be found at healthy sights but at levels that are too low to be clinically relevant. Disease occurs as a result of a shift in the balance of the resident microflora due to a change in the local environmental conditions.

Question 14

Ecological plaque hypothesis

Answer 14

Total amount of dental plaque and specific microbial composition of plaque contribute to the transitions from health to disease. The health-associated plaque is said to be relatively stable and in a state of equilibrium or microbial homeostasis. Then chemical and physical changes happen to the habitat e.g. increased GCF flow which then changes the nutrient status in the periodontal pocket.

Question 15

What is a consequence of the ecological plaque hypothesis?

Answer 15

Periodontal disease can be prevented, not only by targeting the putative pathogens, but also by interfering with the environmental factors that drive the changes in the balance of the microflora.

Question 16

Name the bacterial species in the red complex of periodontal disease.

Answer 16

Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola

Question 17

What is the aetiology of gingivitis?

Answer 17

Accumulation of dental plaque -> gingival inflammation, can be reversed by plaque removal or worsened by systemic factors

Question 18

What is the aetiology of periodontitis?

Answer 18

Colonisation of sub-gingival regions by specific groups of micro-organisms -> expression of virulence factors e.g. proteases, leukotoxin -> destructive immune responses -> loss of periodontal tissue including gingiva, periodontal ligament and alveolar bone

Question 19

How do plaque bacteria cause disease?

Answer 19

Majority of plaque Bactria are commensal in nature and can be removed easily from teeth and tissues with good oral hygiene technique. Red and orange complex organisers produce a variety of virulence factors that initiate periodontal disease and allow its progression. Bacteria do not need to invade tissues and colonise periodontal tissues in order to causes disease. The immune states of the host and effectiveness of the host response are key determinants of disease susceptibility.

Question 20

What is virulence?

Answer 20

Virulence is a measure of the damage induced by the micro-organism.

Question 21

What are virulence factors?

Answer 21

These are microbial determinants that mediate host damage in the context of microbial pathogenicity. They help the bacteria colonise the host at the cellular level.

Question 22

Name some virulence factors.

Answer 22

Surface associated factors- adhesion pili, capsule, adhesins, LPS flagella, surface proteins
Secreted factors- exotoxin, enzymes, iron binding proteins

Question 23

How do bacteria acquire virulence genes?

Answer 23

Bacteria can acquire virulence genes by phages (via transduction) and other mobile genetic elements such as plasmids (via conjugation)

Question 24

What virulence factors have direct toxic effects?

Answer 24

Endotoxins and exotoxins

Question 25

What are endotoxins?

Answer 25

Bacterial endotoxin is produced by all gram negative bacteria, endotoxins consist principally of lipopolysaccharides (LPS), LPS is released from the bacterial cell wall during growth and after cell lysis, LPS is a potent toxin capable of activating complement and macrophages, degranulating neutrophils and stimulating bone resorption

Question 26

What are exotoxins?

Answer 26

Exotoxins are continuously released by certain live bacteria. An example is leukotoxin produced by Aggregatibacter actinomycetemocimitans which inhibits neutrophils and macrophages

Question 27

What are some surface associated virulence factors?

Answer 27

Adhesins, flagella and capsules

Question 28

What are adhesins?

Answer 28

These are microbial components that enable a microbe to attach to host tissues. They are chemically diverse molecules that include proteins, polysaccharides and bacterial cells wall components

Question 29

What are flagella?

Answer 29

These help some bacteria be mobile, they function in attachment and biofilm formation

Question 30

What are capsules?

Answer 30

They protect the microbe against host immune mechanisms, Porphyromonas gingivalis has a capsule which protects it from phagocytosis and intracellular killing

Question 31

What are some enzyme virulence factors?

Answer 31

Enzyme virulence factors include proteases, glucosidases and phospholipases

Question 32

What do enzymes do?

Answer 32

They damage cells and provide nutrients by digesting substrates into smaller components that can be assimilated by microbes.

Question 33

What does Fusobacterium nucleatum do?

Answer 33

It acts as a key bridging organisms for periodontal pathogens such as Porphyromonas gingivalis and Treponema denticola. It is an obligate anaerobe.

Question 34

What is Porphyromonas gingivalis?

Answer 34

A gram negative, strictly anaerobic bacteria which is strongly associated with adult periodontitis and rapidly aggressive periodontitis.

Question 35

What virulence factors does Porphyromonas gingivalis (red complex) produce?

Answer 35

Production of proteases which degrade complement, immunoglobulins and collagen. It also has a capsule.

Question 36

What virulence factors are produced by Tannerlla forsythia (red complex)?

Answer 36

Production of trypsin-like proteases and glycosidase enzymes

Question 37

What virulence factors are produced by Treponema denticola (red complex)?

Answer 37

Production of potent hydrologic names including collagenases and proteases

Question 38

What are some examples of Prevotella species?

Answer 38

Prevotella are strictly anaerobic. Prevotella intermedia and Prevotella nigrescens are black pigmented strains.

Question 39

What virulence factors does Prevotella intermedia include?

Answer 39

Ability to resist phagocytosis and LPS production

Question 40

What virulence factors are associated with Fusobacterium nucleatum?

Answer 40

Production of potent LPS and the production of butyric acid. It is unable to produce hydrolytic enzymes

Question 41

What is Aggregatibacter actinomycetemocomitans?

Answer 41

A facultative gram negative anaerobe. It has been implicated in a particularly aggressive form of periodontal disease in adolescents (localised aggressive periodontitis). It appears to be associated with actively progressive lesions.

Question 42

What are some of the virulence factors associated with Aggregatibacter acinitomycetemcomitans?

Answer 42

Production of collagen are and ability to resist phagocytosis

Question 43

What bacterial interactions and pathogenic synergy take place in the aetiology of periodontal disease?

Answer 43

Bacteria can signal to each other and relay information about the biofilm environment.
Bacterial gene transfer can occur readily within biofilms.
Co-adhesion between bacteria allows organisation of the biofilm architecture.
The extracellular polymeric matrix and the presence of other bacteria within the biofilm is protective.
Microorganisms may be dependent on each other for essential nutrients or bacterial interactions are required for attachment to the acquired enamel pellicle so that bacteria can adhere and resist the removal forces provided by GCF.

Question 44

How do pathogens lead to tissue destruction?

Answer 44

LPS (endotoxin) is particularly important in periodontal disease as it is a component of all gram -ve periodontal pathogens. LPS activates complement and macrophages, degranulates neutrophil and directly stimulates bone resorption.
Leukocidin,a toxin released by Aggregatibacter acitnomycetemcomitans destroys or lyses white blood cells.
Bacterial enzymes such as collagenases break down host proteins.
Bacteria elicit innate and adaptive immune response and the magnitude of these responses determine whether bacteria are eliminated successfully or whether bystander damage occurs.