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Flashcards in GENERAL Deck (62):
1

Describe the 5 steps of Koch's postulates

1. The microorganism is present in every case of the disease but absent from healthy organism
2. The suspected organism must be isolated and grown in a pure culture
3. The same disease must result when the isolated microorganism is inoculated into a healthy host
4. The same microorganism must be isolated again from the diseased host
5. The antibody to the organism should be detected in the patient's serum

2

What does endogenous mean?

Associated with the body

3

What is the term used to describe bacteria associated with the body

Endogenous

4

What does exogenous mean?

Associated with the environment

5

What is the relationship between the bacteria and host if the host does not gain from the association with the bacteria, but is also unharmed, while the bacteria gains advantage?

Commensal

6

What is the relationship between the bacteria and host if they both gain mutual value? Explain how this happens

Mutualistic/Symbiotic.
Organism can produce nutrients or vitamins that can degrade harmful chemicals. Idea of colonisation resistance where endogenous microbial population confer protection against exogenous pathogens

7

Describe a parasitic relationship between bacteria and host

Host is harmed but parasite gains

8

Define pathogen

A microbe that is capable of causing host damage, includes classical pathogens and opportunistic pathogens, and damage produced directly or via the host immune response.

9

Define pathogenicity

Pathogenicity refers to the capacity to cause disease or damage

10

Define virulence

Virulence refers to the capacity of a microbe to cause damage to the host. It is related to an organism's toxigenic potential and invasiveness.

11

What is LD50?

The lethal dose required to kill 50% of the host

12

What is ID50?

The infectious dose required to infect 50% of the hosts.

13

Define virulence factor

A component of a pathogen that enhances its pathogenicity, helping it to damage the host.

14

List the 5 steps of molecular koch's postulates

- A virulence trait should be strongly associated with pathogenic strains of the species
- Inactivation of the gene(s) associated with the virulence trait should decrease pathogenicity
- Restoration of an inactivated/mutant gene with the wild type restores pathogenicity
- The gene is expressed at some point during infection
- Antibodies directed against the gene product protects the host

15

List 2 limitations of koch's postulates.

1. Organism cannot be cultured/isolated - obligate intracellular organisms
2. Unethical to inoculate a human with the pathogen - no model organisms to inoculate since organism is a human pathogen

16

What is an obligate pathogen?

Bacteria that must cause disease in order to be transmitted from one host to another. Bacteria must also infect a host in order to survive as it is incapable of surviving outside of host.

17

What is an opportunistic pathogen?

Bacteria that do not have to cause disease for transmission i.e. can be transmitted from one host to another without having to cause disease. However, in a host whose immune system is not functioning properly, the bacteria can cause an infection that leads to a disease.

18

What are accidental pathogens?

Pathogens whose transmission are prevented or hindered by disease. They can be part of normal flora but not transmitted as a result of disease.

19

Give an example of an obligate pathogen

Treponema Pallidum
Mycobacterium tuberculosis

20

Give an example of an opportunistic pathogen

S. oralis
Actinomyces
S. anginosus

21

Give an example of an accidental pathogen

Bacteroides fragilis
Neisseria meningitides

22

Define plaque

A biofilm of bacteria that grows on surfaces within the mouth, such as the tooth surface.

23

List 3 main components of dental plaque

1. Living and dead bacteria
2. Extra-cellular bacterial products
3. Host compounds (from gingival crevicular fluid + saliva)

24

Define biofilm

Biofilm refers to an aggregation or community of bacteria that grows on surfaces, embedded within a self-produced extracellular matrix.)

25

How many % of bacteria causing human infections exist as biofilm?

65%

26

List 3 properties of a typical biofilm

1. Spatially organized in a 3D structure
2. Bacterial cells are enclosed in extra-cellular matrix
3. Increases habitat range of individual bacteria - confers a selective advantage

27

What is the major non-living component of plaque?

Extracellular Polymeric Substances (EPS) / Glycocalyx

28

How many % of total plaque volume is the Extracellular Polymeric Substance?

30%

29

What is the extracellular polymeric substance composed of?

Host products and bacterial products;
incorporates the gingival and proteins from the crevicular exudate.

30

What is the pre-requisite for bacterial attachment to enamel?

Requires an acquired pellicle

31

Define acquired pellicle

It is the layer of material acquired by a cleaned tooth

32

What is the acquired pellicle made of? (x4)

- mucins
- salivary glycoproteins
- minerals
- immunoglobulins

33

How long does the acquired pellicle take to form?
How long does it take to reach its max thickness?

form within seconds; 90-120 mins for max. thickness

34

What is the function of the pellicle?

Bridges the adhesion of bacteria to enamel

35

Which cell wall component contributes to charge and attachment?

Lipoteichoic acid

36

Define amphipathic molecules
(wrt lipoteichoic acid)

Amphipathic molecules refer to those with one hydrophobic and one hydrophilic end. The hydrophobic (lipid) end is embedded in the membrane while the glycerol phosphate and hydrophilic end is at the outside

37

How does the environment change on adhesion of bacteria to pellicle? (x3)

1. Aerobic to anaerobic environment
2. pH, nutrients, ions, metabolic products
3. New attachment sites, co-aggregation

38

Name 2 extracellular polysaccharide substances

1. Glucans
2. Fructans

39

What are glucans?

Glucose polysaccharides with glucose molecules joined by a(1,3) or a(1,6) links

40

What are fructans?

Fructose polysaccharides with fructose molecules joined by B(2,6) or B(2,1) links

41

What is the enzyme catalyzing the glucan reaction?

Glucosyltransferase

42

State the glucan reaction

sucrose + (glucan)n --> (glucan)n+1 + fructose

43

State the fructan reaction

sucrose + (fructan)n --> (fructan)n+1 + glucose

44

What is the enzyme catalyzing the fructan reaction?

Fructosyltransferase

45

What are adhesins?

Specific molecules on bacterial surface that recognise specific ligands or receptors on tooth surface

46

What are lectins?

Sugar binding proteins that recognise carbohydrate groups and bind them

47

Functions of fimbriae (x2)

1. Adhesion to other bacteria
2. Adhesion to enamel/pellicle

48

Which bacteria dominates at 24h?

Streptococcus (S. Oralis)

49

List the steps of plaque development? (x6)

1. Clean enamel surface
2. Pellicle formation - 2s
3. Pioneer bacteria - 1 min
4. Micro-colonies & Extracellular polysaccharide - 2h
5. Biofilm development - 2h onwards
6. Mature plaque - 48h

50

List the 3 types of adhesion seen in dental plaque

1. Cell-substratum adhesion
2. Homotypic cell-cell adhesion
3. Heterotypic cell-cell adhesion

51

Define homotypic cell-cell adhesion

Interaction of a specific cell with an identical cell

52

Define heterotypic cell-cell adhesion

Adhesion between 2 different type of cells

53

Give 2 examples of heterotypic cell-cell adhesion

1. Actinomyces with Prevotella
2. S. Oralis with Prevotella

54

What are synergistic interactions?

Enzymes secreted / released upon lysis benefits more than 1 species

55

What is homofermentation of glucose?

Conversion of 1 molecule of glucose into 1 fermentation product, which is 2 moles of lactic acid

56

What does heterofermentation of glucose refer to?

Conversion of 1 molecule of glucose into more than 1 fermentation product, namely 1 mole of lactic acid, 1 mole of ethanol and 1 mole of CO2

57

What does protein breakdown in plaque produce? What is the effect?

Production of ammonia gas (NH3) --> Counters the development of low pH for cariogenic activity

58

What are antagonistic interactions?

Competition of substrates between micro-organisms, which can result in the production of bacteriocins to damage competitors

59

Define bacteriocins

A substance, usually a protein, released by one bacteria that kills another, usually by inducing a metabolic block.

60

Name the bacteriocin produced by streptococcus and state their function

Mutacins;
Peptide antibiotics produced by S. Mutans that specifically inhibits the growth of closely related species, that would otherwise compete for the same nutrients.

61

Name 10 components of the enamel/salivary pellicle

1. Mucins
2. Acidic Proline-Rich Proteins (PRPs)
3. Statherin
4. Amylase
5. Lysozyme
6. Albumin
7. Immunoglobulins
8. Glucosyltransferases
9. Glucans
10. eDNA

62

Name 4 reasons for variation found in dental plaque

1. Sites of plaque (supragingival; mainly aerobic gram-positive VS subgingival; mainly anaerobic gram-negative)
2. Time (rapid vs slow build up, and time since last meal)
3. Genetics; Saliva and GCF composition varies from individual to individual
4. Diet (e.g. low carb vs high carbs; low protein vs high protein etc.)