Microbe-host interactions (Oral microbiology)

Question 1

Define ‘infection/colonization’

Answer 1

Acquisition of micro-organism by host

Question 2

Define ‘commensalism’

Answer 2

Infection with no damage to host

Question 3

Define ‘symbiosis/mutualism’

Answer 3

Infection where both host and microbe benefit

Question 4

Define ‘pathogen’

Answer 4

Microbe that damages host

Question 5

Define ‘opportunist pathogen’

Answer 5

Microbe that can onl damage host when defences are weakened

Question 6

Define ‘persistence/latency’

Answer 6

Failure of host to fully eliminate a micro-organism

Question 7

Define ‘chronicity’

Answer 7

Persistence with continued host damage

Question 8

How to identify uncultivatable bacteria:

Answer 8

• Sequence the 16S ribosomal subunit RNA
• 16S RNA is highly conserved but region after it is variable between microorganisms
• Look for patterns in the variable regions

Question 9

Mitochondrial ancestry:

Answer 9

• Eukaryotes engulfed a prokaryote
• Symbiosis where prokaryote produced ATP for eukaryote
• Mitochondria similar to prokaryotes:
  1) similar genetic code
  2) Replicate via binary fission
  3) Prokaryote ribosomes

Question 10

List the four stages of illness

Answer 10

1) Incubation period
2) Prodromal stage
3) illness period
4) Convalescent period

Question 11

Define Infectious dose 50 (ID50)

Answer 11

Number of microorganisms needed to infect 50% of people:

Question 12

Low ID50?

Answer 12

High virulence of the microorganism

Question 13

Define ‘virulence’

Answer 13

Degree which pathogen can cause damage

Question 14

Define ‘virulence factors’

Answer 14

Characteristics of pathogen that contribute to disease-causing process

Question 15

Define ‘pathogenecity islands’

Answer 15

Group of genes encoding for virulence factors; transferred from bacteria to bacteria

Question 16

List the steps to pathogenesis

Answer 16

1) Adherence and colonization
2) Invasion
3) Evasion of host defense
4) Toxins (optional)
5) Replication
6) Host bystander damage (optional)

Question 17

Describe ‘adherence and colonization’

Answer 17

• Entry into host

- virulence factors = pili, capsule, and surface receptors

Question 18

Describe ‘invasion’

Answer 18

• Penetrate through mucous membrane

- virulence factors = proteases, hydrolases, lysins, and toxins

Question 19

Describe ‘evasion of host defense’

Answer 19

• Resist innate/adaptive immunity and coagulation
• virulence factors = Disruption of host immune system, capsules of host membrane, rapid mutations, biofilm formation, etc.

Question 20

Define ‘toxins’

Answer 20

• Toxin = substance that alters the normal metabolism of host cells
• Exotoxin: i) released by growing gram positive bacteria, ii) soluble, heat sensitive proteins
• Endotoxins: i) lipopolysaccharides from gram negative bacteria outer membrane, ii) Disrupt host immune system

Question 21

Define ‘replication’

Answer 21

• requires proteins, carbohydrates, and iron from host

- virulence factors = proteases, haemagglutinins (destroy RBC for iron)

Question 22

Define ‘host bystander damage’

Answer 22

Host’s immune response destroys its own tissue

Question 23

Describe ‘opportunist pathogens’ and give two examples

Answer 23

• Not pathogenic until host become immunocompromised

- e.g. Clostridium difficile and candida albicans

Question 24

What are commensal organisms

Answer 24

• Inhabit skin, oral, respiratory and GI tracts
• Prevent colonization of more pathogenic organisms
• synthesize metabolites/nutrients

Question 25

Commensal organisms on the skin

Answer 25

• environment is slightly acid pH
• High salt in environment
• Low water environment
• Most bacteria found on near sweat/oil glands
• Mostly actinobacteria (organisms)

Question 26

Commensal organisms in gut

Answer 26

• environment has acidic pH in stomach
• Alkaline environment in small intestine
• High water and nutrients in environment
• No oxygen here
• Inhibitory secretion from pancreas
• Mostly bacteroides (organisms)

Question 27

commensal organisms in oral

Answer 27

• Variable pH
• variable temperature
• Oxygen, but not in all parts of mouth
• High moisture
• Composition of saliva
• Biofilm forms on teeth: teeth are the only structure that isn’t shed
• Hard and soft surfaces
• Mechanical perturbation
• Competition from other bacteria
• Transmission rate can be high
• Mostly Firmicutes (organisms)