Flashcards in GENERAL Deck (62):
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
What does endogenous mean?
Associated with the body
What is the term used to describe bacteria associated with the body
What does exogenous mean?
Associated with the environment
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?
What is the relationship between the bacteria and host if they both gain mutual value? Explain how this happens
Organism can produce nutrients or vitamins that can degrade harmful chemicals. Idea of colonisation resistance where endogenous microbial population confer protection against exogenous pathogens
Describe a parasitic relationship between bacteria and host
Host is harmed but parasite gains
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.
Pathogenicity refers to the capacity to cause disease or damage
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.
What is LD50?
The lethal dose required to kill 50% of the host
What is ID50?
The infectious dose required to infect 50% of the hosts.
Define virulence factor
A component of a pathogen that enhances its pathogenicity, helping it to damage the host.
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
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
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.
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.
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.
Give an example of an obligate pathogen
Give an example of an opportunistic pathogen
Give an example of an accidental pathogen
A biofilm of bacteria that grows on surfaces within the mouth, such as the tooth surface.
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)
Biofilm refers to an aggregation or community of bacteria that grows on surfaces, embedded within a self-produced extracellular matrix.)
How many % of bacteria causing human infections exist as biofilm?
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
What is the major non-living component of plaque?
Extracellular Polymeric Substances (EPS) / Glycocalyx
How many % of total plaque volume is the Extracellular Polymeric Substance?
What is the extracellular polymeric substance composed of?
Host products and bacterial products;
incorporates the gingival and proteins from the crevicular exudate.
What is the pre-requisite for bacterial attachment to enamel?
Requires an acquired pellicle
Define acquired pellicle
It is the layer of material acquired by a cleaned tooth
What is the acquired pellicle made of? (x4)
- salivary glycoproteins
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
What is the function of the pellicle?
Bridges the adhesion of bacteria to enamel
Which cell wall component contributes to charge and attachment?
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
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
Name 2 extracellular polysaccharide substances
What are glucans?
Glucose polysaccharides with glucose molecules joined by a(1,3) or a(1,6) links
What are fructans?
Fructose polysaccharides with fructose molecules joined by B(2,6) or B(2,1) links
What is the enzyme catalyzing the glucan reaction?
State the glucan reaction
sucrose + (glucan)n --> (glucan)n+1 + fructose
State the fructan reaction
sucrose + (fructan)n --> (fructan)n+1 + glucose
What is the enzyme catalyzing the fructan reaction?
What are adhesins?
Specific molecules on bacterial surface that recognise specific ligands or receptors on tooth surface
What are lectins?
Sugar binding proteins that recognise carbohydrate groups and bind them
Functions of fimbriae (x2)
1. Adhesion to other bacteria
2. Adhesion to enamel/pellicle
Which bacteria dominates at 24h?
Streptococcus (S. Oralis)
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
List the 3 types of adhesion seen in dental plaque
1. Cell-substratum adhesion
2. Homotypic cell-cell adhesion
3. Heterotypic cell-cell adhesion
Define homotypic cell-cell adhesion
Interaction of a specific cell with an identical cell
Define heterotypic cell-cell adhesion
Adhesion between 2 different type of cells
Give 2 examples of heterotypic cell-cell adhesion
1. Actinomyces with Prevotella
2. S. Oralis with Prevotella
What are synergistic interactions?
Enzymes secreted / released upon lysis benefits more than 1 species
What is homofermentation of glucose?
Conversion of 1 molecule of glucose into 1 fermentation product, which is 2 moles of lactic acid
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
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
What are antagonistic interactions?
Competition of substrates between micro-organisms, which can result in the production of bacteriocins to damage competitors
A substance, usually a protein, released by one bacteria that kills another, usually by inducing a metabolic block.
Name the bacteriocin produced by streptococcus and state their function
Peptide antibiotics produced by S. Mutans that specifically inhibits the growth of closely related species, that would otherwise compete for the same nutrients.
Name 10 components of the enamel/salivary pellicle
2. Acidic Proline-Rich Proteins (PRPs)