Microbe-host interactions (Oral microbiology) Flashcards
Define ‘infection/colonization’
Acquisition of micro-organism by host
Define ‘commensalism’
Infection with no damage to host
Define ‘symbiosis/mutualism’
Infection where both host and microbe benefit
Define ‘pathogen’
Microbe that damages host
Define ‘opportunist pathogen’
Microbe that can onl damage host when defences are weakened
Define ‘persistence/latency’
Failure of host to fully eliminate a micro-organism
Define ‘chronicity’
Persistence with continued host damage
How to identify uncultivatable bacteria:
- 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
Mitochondrial ancestry:
- 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
List the four stages of illness
1) Incubation period
2) Prodromal stage
3) illness period
4) Convalescent period
Define Infectious dose 50 (ID50)
Number of microorganisms needed to infect 50% of people:
Low ID50?
High virulence of the microorganism
Define ‘virulence’
Degree which pathogen can cause damage
Define ‘virulence factors’
Characteristics of pathogen that contribute to disease-causing process
Define ‘pathogenecity islands’
Group of genes encoding for virulence factors; transferred from bacteria to bacteria
List the steps to pathogenesis
1) Adherence and colonization
2) Invasion
3) Evasion of host defense
4) Toxins (optional)
5) Replication
6) Host bystander damage (optional)
Describe ‘adherence and colonization’
- Entry into host
- virulence factors = pili, capsule, and surface receptors
Describe ‘invasion’
- Penetrate through mucous membrane
- virulence factors = proteases, hydrolases, lysins, and toxins
Describe ‘evasion of host defense’
- Resist innate/adaptive immunity and coagulation
- virulence factors = Disruption of host immune system, capsules of host membrane, rapid mutations, biofilm formation, etc.
Define ‘toxins’
- 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
Define ‘replication’
- requires proteins, carbohydrates, and iron from host
- virulence factors = proteases, haemagglutinins (destroy RBC for iron)
Define ‘host bystander damage’
Host’s immune response destroys its own tissue
Describe ‘opportunist pathogens’ and give two examples
- Not pathogenic until host become immunocompromised
- e.g. Clostridium difficile and candida albicans
What are commensal organisms
- Inhabit skin, oral, respiratory and GI tracts
- Prevent colonization of more pathogenic organisms
- synthesize metabolites/nutrients
Commensal organisms on the skin
- environment is slightly acid pH
- High salt in environment
- Low water environment
- Most bacteria found on near sweat/oil glands
- Mostly actinobacteria (organisms)
Commensal organisms in gut
- 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)
commensal organisms in oral
- 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)
